Cell Division and Genetics Lecture 12

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Questions and Answers

What is the primary purpose of mitosis in the human life cycle?

To produce unique offspring

To increase genetic variation

To repair and renew damaged cells (correct)

To create gametes for reproduction

Which cells will undergo meiosis during the human life cycle?

Skin cells

Muscle cells

Gametes (sperm and egg cells) (correct)

Nerve cells

During which process do chromosomes replicate to ensure genetic consistency in daughter cells?

Meiosis

Fertilization

Mitosis (correct)

Chromosome segregation

What is the resulting chromosome number in a zygote after fertilization?

46 chromosomes Signup and view all the answers

What happens to brain neurons after development is complete?

They remain mitotically inactive Signup and view all the answers

Which statement about homologous chromosomes is true?

They carry the same genes but may have different alleles Signup and view all the answers

What ensures genetic diversity in offspring during sexual reproduction?

Meiotic division and random assortment of chromosomes Signup and view all the answers

Which of the following terms describes the genetic makeup of an organism?

Genotype Signup and view all the answers

What is the outcome of Turner syndrome in individuals with this genetic condition?

Underdeveloped internal organs and sterility Signup and view all the answers

Which genetic combination is associated with Klinefelter syndrome?

XXY Signup and view all the answers

What characterizes dominant alleles in terms of gene expression?

Always expressed when present Signup and view all the answers

Which statement is true regarding homologous chromosomes?

They contain the same number of genes. Signup and view all the answers

What is indicated by a genotype of 'Ee' for a gene controlling eye color?

Brown eye color will be expressed. Signup and view all the answers

Nondisjunction during cell division leads to which of the following outcomes?

Gained or lost chromosomes in gametes Signup and view all the answers

Which of the following describes alleles?

They are different variations of a gene. Signup and view all the answers

In genetics, what does the term 'traits' refer to?

Physical expressions resulting from genes Signup and view all the answers

What is the primary purpose of mitosis in human cells?

For growth and development Signup and view all the answers

Which of the following best describes homologous chromosomes?

Pairs of chromosomes that share the same genes Signup and view all the answers

What is the result of nondisjunction during meiosis?

Gametes with an abnormal number of chromosomes Signup and view all the answers

How many unique autosomal chromosomes do humans have in their somatic cells?

22 Signup and view all the answers

Which of the following statements about gametes is true?

They contain all unique kinds of chromosomes. Signup and view all the answers

In terms of genetic inheritance, what does it mean for two alleles to be homozygous?

They express the same phenotypes. Signup and view all the answers

What happens during the process of meiosis that differs from mitosis?

Homologous chromosomes pair and exchange genetic material. Signup and view all the answers

Which type of disorder can result from an abnormal number of chromosomes due to nondisjunction?

Down syndrome Signup and view all the answers

Study Notes

Lecture 12: Cell Division & Intro to Genetics

Today's Lecture Topics: Familiarizing with terminology, Importance of Cell Division, Human Life Cycle, Mitosis, Meiosis, Chromosomal disorders, Introduction to genetics.
Reading Assignment: Chapter 19
Chromosomes and DNA: Chromosomes are individual DNA molecules located within a cell's nucleus. Specific regions on chromosomes are called genes. Genes are instructions that determine traits.
Chromosome Number in Cells:
- Tissue cells (e.g., muscle, bone, skin) have 46 chromosomes (two sets of 23 unique chromosomes, one from each parent)
- Gametes (sperm and egg cells) have 23 chromosomes (one unique set).
Karyotype: A profile of a person's chromosomes arranged from largest to smallest. Karyotypes are used to diagnose chromosomal disorders. This example is from a tissue cell, not a gamete.
Autosomal & Sex Chromosomes: There are 22 unique autosomal chromosomes and the sex chromosomes. A tissue cell has two copies of each autosomal chromosome and two sex chromosomes (can be the same or different, determining sex).
Homologous Chromosomes: Pairs of chromosomes that share the same genes are termed homologous. Tissue cells have 2 sets (one from each parent) of 23 unique chromosome pairs (total of 46 chromosomes).
Male vs Female Karyotype: A tissue cell karyotype for a male has one X and one Y chromosome, while a female's has two X chromosomes.

Cell Division

Reasons for Cell Division:
- Reproduction
- Growth and development
- Repair and renewal of tissues.
Mitosis: Cell division that results in two genetically identical daughter cells.
- Crucial in growth, development, renewal, and repair of tissues.
- DNA replication occurs before, creating identical copies of each chromosome that remain attached.
- Replicated chromosomes align, separating, and moving to opposite ends of the cell.
- After cell division, each daughter cell gets a copy of the original chromosomes.
Stem Cells: Cells in the body that continually undergo mitosis to replenish damaged or lost cells, such as in skin.
- Some specialized cells, like mature brain neurons don’t undergo mitosis.

Meiosis

Gamete Production: Meiosis is a cell division process important for producing gametes (sperm and egg cells) needed for sexual reproduction.
Meiosis and Chromosome Number: Meiosis reduces the number of chromosomes in each daughter cell, to half the number of the original stem cell, from 46 to 23.
Conception: One sperm cell with 23 chromosomes fertilizes one egg cell with 23 chromosomes, forming a zygote (new cell).
Zygote Growth: The zygote grows through repeated cell divisions, increasing the number of cells and copying the chromosomes in each new cell precisely.
Why Meiosis is Essential: If eggs and sperm had 46 chromosomes, the child would have 92 (a doubling of the number of chromosomes) in each cell, and the chromosome numbers would rapidly increase through successive generations.
Job of Meiosis: Meiosis converts cells with two sets of chromosomes (46) into gametes (egg or sperm) with only one set (23).

Chromosomal Disorders

Nondisjunction: Errors in meiosis can cause nondisjunction, where chromosomes don't separate properly.
Consequences of Nondisjunction: These abnormalities in gametes (egg or sperm cells) result in a zygote with the incorrect number of chromosomes.
Down Syndrome: A common genetic disorder caused by an extra copy of chromosome 21 resulting from nondisjunction. People with Down syndrome often have distinctive physical features and developmental delays.
Turner Syndrome: A genetic disorder occurring in females, caused by having only one X chromosome. This causes the development of underdeveloped internal sex organs and sterility.
Klinefelter Syndrome: A genetic condition in males where there are extra (one or more) X chromosomes which results in underdeveloped testes, sterility, and some secondary female sex characteristics at puberty.

Genetics

What is Genetics?: The study of heredity; the chromosomes we inherit from our parents contain genes that determine traits.
Genes: The basic unit of heredity.
- Each gene is a section of a chromosome that gives instructions for making proteins. Proteins that affect structure or function in the body.
Alleles: Different variations of a gene (different instructions for the same trait). For example, different eye colors.
Genotype: The combination of alleles an individual has for a particular gene. Example: EE (homozygous dominant), Ee (heterozygous), or ee (homozygous recessive).
Phenotype: The observable trait, the result of the genotype. Examples: brown eyes, freckles.
Dominant vs Recessive Alleles: Some alleles are dominant, and their traits are shown in the phenotype, as long as one is present, while others are recessive, and their traits are expressed only when two recessive copies are present.

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Description

Explore the fundamental concepts of cell division and genetics in this lecture. Discover the significance of mitosis and meiosis, chromosomal disorders, and how genetic traits are inherited. Familiarize yourself with key terminology and the human life cycle as you dive into the world of chromosomes and DNA.