From Haploid to Diploid IB DP Biology SL/HL PDF

 TO P I C D 3  0   (https://intercom.help/kognity)  Overview D3. Continuity and change: Organisms / D3.2 Inheritance...

 TO P I C D 3  0   (https://intercom.help/kognity)  Overview D3. Continuity and change: Organisms / D3.2 Inheritance 〈 CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- hl2-d- From haploid to diploid S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422- D3.2.0 The big picture cid- D3.2.1: Fusion of haploid gametes in parents to form a diploid zygote D3.2.2: Methods for conducting genetic crosses in flowering plants  251763/ov  D3.2.1-2 From haploid to diploid  D3.2.3-7 Expression of phenotypes  Table of   Learning outcomes D3.2.8-10 Allele combinations contents  By the end of this section you should be able to:  D3.2.11-13 Genetics of the Y chromosome Notebook  Outline that haploid cells (with a single copy of a gene) produced by each parent can fuse to form a diploid D3.2.14-15 Variation in populations zygote with two copies of a gene.   D3.2.16-17 Unlinked genesmethods (HL) Glossary Explain for how flowering plants are genetically crossed.   D3.2.18-21 Distinguish Linked genes (HL) between genotype (combination of inherited alleles) and phenotype (observable traits resulting Reading  from genotype plus environmental factors). assistance D3.2.22 Summary and key terms  D3.2.23 Checklist  D3.2.24 Investigation Unique you! Reflection D3.2.25 You may have been told that you look more like your mother, but your sister has some traits similar to your father. So, why can o spring sometimes resemble one parent more than the other if the o spring are always an equal blend of both parents? We will see why this can happen during this section. In nature, some organisms reproduce asexually, resulting in o spring that are genetically identical clones. In contrast, eukaryotic plants and animals that have a sexual life cycle share a common pattern of inheritance which results in increasing the variation in a population. The o spring produced have % of the genetic material from each parent. However, unless you are a monozygotic twin, your genetic makeup is speci c to you and not the same as that of your sibling, even with the same parents. Once an individual is at sexual maturity, cells within specialised organs called gonads will start to undergo a certain kind of cell division called meiosis. The gonads contain cells whose nuclei have pairs of chromosomes. As described in subtopic D. (/study/app/ib-biology-hl -d-period/sid- -cid- /book/big-picture-id- /), the cells divide twice during meiosis and the unique cells produced are given the term gametes. These are known as haploid (n) as they have only one copy of each chromosome from one of the parents. The gametes are highly specialised with speci c features. Adaptations of human male and female gametes are noted in subtopic B. (/study/app/ib-biology-hl -d-period/sid- -cid- /book/big-picture-id- /). On their own, these gametes cannot generate a new individual. Two gametes (one from the male parent and one from the female parent) fuse together to form a diploid ( n) zygote that now contains an equal amount of genetic information from both parents. In owering plants, such as the pea (Figure ), the male and female gametes are o en present in the same plant; such plants are described as being hermaphroditic.  〈 All topics 〉   TO P I C D 3  (https://intercom.help/kognity) Overview CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422- cid- 251763/ov       Credit: Diane Miller, Getty Images     Figure 1. The flower of the garden pea plant. Mendel’s experiments A monk named Gregor Mendel ( – ) from an area now found in the Czech Republic, conducted numerous plant- breeding experiments over many years using the humble pea (Pisum sativum). He observed ower colour along with the texture and colour of pea seeds and pods (Figure ). His experiments are so important that he is o en referred to as the ‘father of genetics’.   TO P I C D 3  (https://intercom.help/kognity) Overview CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422- cid- 251763/ov           Figure 2. Mendel predicted the inheritance of various traits by observing many pea crosses. To appreciate his experiments, we should understand the structure of a ower.   The male part of the ower is referred to as the stamen and comprises an elongated anther, held up by a thin lament.  (https://intercom.help/kognity) Overview The anther contains the male gametes called pollen. The female part of the ower is the pistil and has a swollen base TO P I C D 3 CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- called an ovary that surrounds the female gametes known as ovules. A style extends from the ovary and terminates in a hl2-d- S U B TO P I C D 3. 2 structure called I N H E R I TA N C E the stigma. When the pollen grains are mature, the anther will break open to reveal them. period/sid 422- cid- 251763/ov In order for the male and female gametes to come together, the pollen needs to move to the stigma. When it arrives there,  it grows a pollen tube, which carries the pollen containing the haploid nucleus all the way down the hollow style to an  ovule of the ovary. If pollen from one plant lands on the stigma of the same plant it is called self-pollination. If pollen from  one plant lands on another plant of the same species, it is cross-pollination. Both types of pollination are illustrated in Figure. Pollen can only grow a pollen tube if it lands on the same species. However, the pollen/stigma interaction is  highly selective and will try to stop pollen from the same plant growing a pollen tube, preferentially allowing pollen from  a di erent plant of the same species. This improves the genetic variation.        TO P I C D 3  (https://intercom.help/kognity) Overview CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422- cid- 251763/ov           Figure 3. Self-pollination occurs between the same flower or between different flowers on the same plant. Cross-pollination occurs between different plants of the same species. In his experiments, Mendel crossed many pea plants by selecting the pollen from one plant and brushing it onto the stigma of another plant. He was able to rst observe and later predict the inheritance of di erent pea ower and pea seed traits. For example, he showed that when true-breeding parents for traits such as round seeds were bred with true- breeding parents for wrinkled seeds, they would result in o spring that produced only one form of these traits (e.g. round seeds). The parent generation is termed the P generation and the o spring are called the lial (F) generation. The   rst generation is therefore called the F generation. If two members of the F generation are subsequently bred together,  (https://intercom.help/kognity) Overview this would give rise to the F generation which would then possess some physical characteristics not seen in the F TO P I C D 3 CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- generation (e.g. wrinkled seeds). This is illustrated in Figure. hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422- cid- 251763/ov           Figure 4. Mendel conducted breeding experiments with true-breeding pea plants to observe the F1 and F2 generations. A graphical way of predicting such genetic crosses is using a Punnett grid (also called a Punnett square). These will be explained later in subtopic D. (/study/app/ib-biology-hl -d-period/sid- -cid- /book/the-big-picture-id- /). Breeding climate-smart crops Genetic breeding experiments between two related species are commonly used to generate new varieties of crops. Speci c individuals can be carefully selected to ensure that the o spring have desired characteristics. As the world strives to achieve the UN Sustainable Development Goal # (https://www.un.org/sustainabledevelopment/hunger/) of   Zero Hunger, scientists around the world are focused on breeding plants that are able to cope with climate change,  (https://intercom.help/kognity) Overview extreme TO P I C D 3 weather, drought or ooding. CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422-  International Mindedness cid- 251763/ov  Sustainable development  Various academic institutions are examining how crops can be bred to be ‘climate-smart’. The International Wheat and Maize Improvement Center (CIMMYT (https://www.cimmyt.org/news/historic-release-of-six-improved-wheat-  varieties-in-nepal/)) has developed drought- and heat-resilient wheat that is also high in zinc. It is hoped that this will improve the situation in Nepal by providing a much-needed nutrient in a crop that can cope with climate  changes.  A virus-resistant breed of potato called Unica has been developed to thrive in flood-prone and high heat areas of  Kenya.  In Saudi Arabia, salt-tolerant Galapagos tomatoes have been bred with domesticated tomato plants that give nice juicy fruits to combine both these traits. The resultant plants can potentially be watered with sea water to provide  a means of irrigation without the need for valuable fresh water. See Video 1 for more information on this.  Breeding Salt Tolerant Crop Plants  Video 1. Breeding salt tolerant crops. These examples could all help mitigate food insecurity. Genotypes and phenotypes In any eukaryotic cell, pairs of homologous chromosomes exist; one chromosome comes from the mother and the other from the father. Along the length of the chromosome are stretches of DNA called genes, many of which encode speci c proteins. These genes are in identical positions on each of the chromosomes and so an individual will therefore have two copies of the gene (one from each parent) (Figure ).   TO P I C D 3  (https://intercom.help/kognity) Overview CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422- cid- 251763/ov           Figure 5. A pair of homologous chromosomes showing the presence of a gene in the same position on both chromosomes. However, the two genes may di er from each other by a few bases. These di erent forms of a gene are called alleles and this allele combination is called the genotype. When a gene has two identical alleles, this is known as homozygous. When the two alleles are di erent from one another, it is referred to as heterozygous. This idea is illustrated in Figure. Figure 6. Different genotypes: homozygous and heterozygous. Genotypes can be hard to determine but some physical traits are easily visualised and are caused by the genotype an individual possesses. For example, hitchhiker’s thumb is a genetically determined condition. It is thought to be inherited in an autosomal recessive manner, meaning that a child has to inherit two copies of the gene for hitchhiker’s thumb - one from each parent. However, there is still much to be learned regarding this particular trait. For example, are just two alleles involved? Is there just one form of Hitchiker's Thumb? Only time and new research will tell. In contrast, physical traits like having a tattoo are things that have been done to an individual and are not a result of the genotype. The outward expression of the combination of the alleles along with the in uence of environmental factors is known as the phenotype. Some traits, like our skin colour, are a combination of both genetics and environment; in this case, how much we expose our skin to the sun. Figure illustrates the three di erent types of trait.   TO P I C D 3  (https://intercom.help/kognity) Overview CONTINUITY AND CHANG E: ORGANISMS (/study/ap biology- hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422- Credit: Eugenio cid- Marongiu, Getty 251763/ov  Images          Source: 'Hitchiker's thumb (https://commons.wikimedia.org/wiki/File:Hitchhiker%27s_thumb.jpg)' by Alexis Lours is licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) Credit: John White Photos, Getty Images   Figure 7. Three different traits: hitchhiker's thumb is a genetic trait; having a tattoo is an environmental trait; sunburn is an (https://intercom.help/kognity) Overview TO P I C D 3 CONTINUITY AND CHANG E: ORGANISMS example of a trait influenced by genetics and the environment. (/study/ap biology- hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E period/sid 422- Try the activity below alongside Interactive to help with your understanding of parts of a ower and the processes of cid- 251763/ov pollination  and fertilisation. Dictionary    Activity  IB learner profile attribute: Inquirer  Approaches to learning: Research skills – Comparing, contrasting and validating information  Time required to complete activity: 20 minutes  Activity type: Individual activity   Your task  Step 1: In Interactive 1 drag and drop the correct terms to label the insect-pollinated flower. Filament Petal Pistil Sepal Style Anther Stigma Ovule Ovary Stamen  Check  Interactive 1. Parts of a flower. Step 2: For the parts of a flower involved in pollination and fertilisation, research the number of chromosomes in these cells. Copy and complete Table 1 with the information you find out. Table 1. Chromosomes in cells. Number of copies of Haploid (n) or Cell type each chromosome diploid (2n) petal   Number of copies of Haploid (n) or  (https://intercom.help/kognity) Overview TO P I C D 3 Cell type CONTINUITY AND CHANG E: ORGANISMS each chromosome diploid (2n) (/study/ap biology- hl2-d- S U B TO P I C D 3. 2 I N H E R I TA N C E pollen period/sid 422- cid- ovule 251763/ov   zygote   Discuss your findings with the class.   Reset   You have completed this section with 5 questions  〈 Previous(/study/app/ib-biology-hl2-d-period/sid-422-cid-251763/book/the-big-picture-id-43244/) Next 〉(/study/app/ib-biology-hl2-d-period/sid-4  