Reproduction and Heredity

Asexual Reproduction

• Requires only one parent.
• Does not involve sex cells.
• Offspring are produced through cell division.
• Offspring are genetically identical to the parent, possessing the same DNA.
• Several types occur in both plants and animals.

Types of Asexual Reproduction

• Binary Fission involves an organism splitting in half, resulting in two identical daughter cells, which are initially half the size of the parent but grow and divide. Commonly seen in bacteria.
• Budding involves a small bud growing out of the parent cell, creating two cells of different sizes but with identical DNA. The bud eventually breaks off and grows independently, as seen in yeast and hydra.
• Regeneration is the process of repairing or regrowing lost body parts through cell division of leftover cells, observed in lobsters, starfish, and lizards.

Sexual Reproduction

• Needs two parents, each contributing half of the genetic information to the offspring.
• Offspring inherit and share characteristics from both parents.

Fertilization Types

• Internal Fertilization occurs inside the female, where the egg is fertilized by sperm. Seen in mammals, birds, reptiles, insects, and spiders.
• External Fertilization happens outside the female, with the female laying eggs and the male fertilizing them externally. Commonly observed in fish and some amphibians, as well as plants and fungi via pollen and spores.

Seeds in Plants

• Seeds result from sexual reproduction in most plants.
• A seed contains an embryo, a food supply, and a protective seed coat.
• Angiosperms are flowering plants, while Gymnosperms bear seeds inside cones.
• The inside of a flower has four parts: petals, sepals, stamen (male), and pistil/carpel (female).

Stamen

• The stamen (male part) comprised of the anther and filament.
• Anther is a sac-like structure that produces and stores pollen
• The filament supports the anther.

Petals

• The petals attract insects for pollination due to their large size.
• Pollen sticks to the insect and is dispersed to other flowers when the petals are enclosed so that the insect makes contact with the pollen.
• Removing the anthers can prevent self-pollination.
• Grass flowers expose pollen for wind dispersal and have feathery stigmas to catch pollen.
• Grass flowers are typically small and not brightly colored.

Pollination

• Pollination is the process of transferring pollen from the male part (anther) to the female part (stigma) of a flower.

Pistil

• The pistil (female part) consists of the stigma, style, and ovary.
• Stigma is the topmost part of a flower.
• Style is the tube connecting the stigma to the ovary.
• Ovary contains ovules where seed formation occurs.

Seed Dispersal by Wind

• Seeds are light and small, facilitating dispersal by light breezes.
• Smooth seeds roll easily on the ground.
• Some seeds have papery wings, parachutes, or long hairs for air currents.
• Some plants break off when dry, scattering seeds as they roll.

Seed Dispersal by Animals

• Hooked fruits attach to animal fur or clothing and fall off later.
• Succulent, bright-colored fruits attract birds, insects, and animals that eat the fleshy part.
• Some animals carry away large fruits, eat the flesh, and discard the seeds.

Sexual Reproduction and Gametes

• A gamete is a reproductive cell of an animal or plant.
• Female gametes are called ova or egg cells, and male gametes are called sperm.
• Ova and sperm are haploid cells, carrying only one copy of each chromosome.
• During fertilization, gametes fuse to form a zygote.
• Fertilization is the union of a sperm nucleus with an egg nucleus to form the primary nucleus of an embryo.

Sexual Development

• At birth, sex organs distinguish males and females (primary sexual characteristics).
• Puberty involves maturation and release of gametes (egg and sperm), and developments to allow reproduction.

Cells

• Cells serve to provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions
• Basic unit of life.
• The human body has trillions of cells.

Parts of a Cell

• Cytoplasm
• Cytoskeleton
• Endoplasmic reticulum (ER)
• Golgi apparatus
• Lysosomes and peroxisomes
• Mitochondria
• Nucleus
• Plasma membrane
• Ribosomes

Nucleus

• The nucleus contains the cell's command center, sending directions to the cell to grow, mature, divide, or die.
• It also houses DNA (deoxyribonucleic acid), the cell's hereditary material.
• The nucleus is surrounded by a membrane called the nuclear envelope, which protects the DNA and separates the nucleus from the rest of the cell.

DNA

• DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms.
• DNA information is stored as a code made up of different chemicals.
• Key property is its ability to replicate, ensuring each new cell gets an exact copy during cell division.
• Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases.
• DNA is stored as a code made up of different base pairs.
• Adenine pairs with Thymine.
• Guanine pairs with Cytosine.
• The sequence of bases determines the information for building and maintaining an organism.
• DNA is packed into chromosomes, thread-like structures within the nucleus with a double helix shape.

Chromosomes

• Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
• Humans have 23 pairs of chromosomes (46 total) in each cell.
• Twenty-two pairs are autosomes, which look the same in males and females.

Genes

• A gene is a small section of DNA on a chromosome that codes for a particular sequence of amino acids to make a specific protein.
• It is the unit of heredity, and may be copied and passed to the next generation.

Alleles

• Alleles are different versions of the same gene.
• Gene specifies trait, allele specifies form gene takes.
• Dominant alleles which are always expressed - represented by a capital letter, for example, F.
• Recessive alleles which are only expressed if two copies are present - represented by a lower-case letter, for example f.
• Homozygous alleles are both identical for the same characteristic, for example AA or aa.
• Heterozygous alleles are different alleles for the same characteristic, for example Aa.
• A karyotype shows an individual’s complete set of chromosomes.

Sex Chromosomes

• Sex is determined by the two sex chromosomes, X and Y.
• Males carry chromosomes XY and females XX.
• The mother can only pass on an X chromosome
• The father can pass on either an X or a Y chromosome
• The inheritance of se can be shown using a genetic diagram (known as a Punnett square), with the X and Y chromosomes taking the place of the alleles usually written in the boxes.
• Males determine the sex of offspring.

Variation

• Variation is all the differences that exist in a population of the same species.
• Differences are caused by: genetic variation & environmental variation.

Genetic Variation

• These are differences between individuals that are inherited from parents, such as the colour of your eyes, hair and skin.
• Tall parents will pass genes to their children for hair type.
• Brown eyes parents will pass genes to their children for eye color.

Environmental Variation

• These are differences between individuals that are not inherited but caused by the environment that the organisms live in.
• ‘Environmental’ simply means ‘outside of the organism’ and so can include factors like climate, diet, culture, lifestyle and accidents during lifetime.
• An accident may lead to scarring on the body.
• Eating too much and not leading an active lifestyle will cause weight gain
• Being raised in a certain country will cause you to speak a certain language with a certain accent
• A plant in the shade of a big tree will grow taller to reach more light.

Discontinous Features

• Discontinuous variation is usually caused by genetic variation alone.
• Continues features often vary because of a combination of genetic and environmental causes.

Family Pedigrees

• Family pedigree diagrams are used to trace the pattern of inheritance of a specific characteristic (usually a disease) through generations of family.
• This can be used to work out the probability that someone in the family will inherit that genetic disorder.
• Pedigrees show the presence or absence of a trait as it relates to the relationship among parents, offspring, and siblings.

Inheritance

• Inheritance is the process by which genetic information is passed from parent to offspring.
• The information is passed by the form of DNA
• DNA is located in the chromosomes of the cell nucleus
• Chromosomes are made up of DNA, which contains genetic information in the form of genes
• A Gene is a a length of DNA that codes for a protein
• Genes come in different versions known as alleles

Gene and Allele Count

• Each human contains 46 chromosomes
• A Male has XY chromosomes and a female has XX chromosomes
• A Gene is the physical expression of the genotype
• Half of sperm contains X chromosomes and the other half contains Y chromosomes
• And the egg cell carries the X chromosome

Definitions

• Homozygous is having two copies of the same allele.
• A Recessive Allele is when two copies of an Allele are needed to have an effect - The trait will only show up when both copies of the Allele are the same
• Heterozygous is when when you have two different Alleles for a Gene - its when you have one Dominant Allele and one Recessive Allele like Bb
• Genotype is the Alleles present for a certain feature (it is the Genetic code that determines that trait).
• Dominant Allele is when one copy of an Allele is needed to have an effect (it shows the trait even with one copy)
• Phenotype is the physical trait of a characteristic like height or hair color it's what shows from your Genotype
• Differences: Genes, Environment, Genetic variation

Darwin's Theory of Evolution

• Charles Darwin was an English naturalist that studied variation in plants, animals and fossils during a 5 year voyage around the world in the 19th century.
• Darwin visited four continents on the HMS Beagle ship.
• On the Galapagos Islands, Darwin studied many species that were unique to the islands, but similar to species elsewhere.
• These observations led him to consider the possibility that species can change over time.
• Evolution is a change in the inherited characteristics of a population over time through the process of natural selection, which may result in the formation of new species.
• Natural selection is a process where organisms that are adapted better to an environment will survive and reproduce.
• The advantageous alleles of this variant organism are passed onto offspring.
• Over many generations, the process of natural selection leads to evolution occurring.

Darwins Proposal

• Individual organisms within a particular species sow a wide range of variation for a characteristic.
• Individuals with characteristics most suited to the environment are more likely to survive to breed successfully.
• The characteristics that have enabled these individuals to survive are then passed on to the next generation.
• Over time the rats adapted to the warfarin giving them immunity.

Key Terms for Genetics

• Heterozygous Bb
• Homozygous recessive bb
• Homozygous dominant BB also Bb

Questions about asexual and sexual reproduction, fertilization, plant reproduction, and basic genetics concepts like phenotypes and pedigrees.