EXAM 4

Question 1

What are the four reasons for mitosis to occur, and what is the only reason for meiosis to occur?

Answer 1

4 reasons for cell division in mitosis:
- for growth
- repair damage cells
- replace old or worn out cells
- to reproduce (in single-celled organisms)

Only reason for meiosis to occur:
- to produce gametes (sex cells)

Question 2

Why is it important for the number of chromosomes to be reduced in meiosis, from 46 to 23?

Answer 2

Most of our cells are diploid (46 chromosomes/2n)
– Our gametes are haploid (23 chromosomes/n)
- for offsprings

Question 3

Mitosis or meiosis?
a. Which one produces two identical diploid daughter cells?
b. Which one produces four haploid daughter cells (and each cell is different)?
c. Which one must happen for sexual reproduction?
d. Which one must happen for asexual reproduction?

Answer 3

a. Which one produces two identical diploid daughter cells?

Mitosis
b. Which one produces four haploid daughter cells (and each cell is different)?

Meiosis
c. Which one must happen for sexual reproduction?

Meiosis
d. Which one must happen for asexual reproduction?

Mitosis

Question 4

What is happening during metaphase and anaphase of mitosis?

Answer 4

Metaphase: The chromosomes line up in the
middle of the cell (no more nuclear membrane)

Anaphase: Each chromosome’s pair of sister
chromatids begin to separate; one set of sister
chromatids is pulled toward one end of the cell,
while the other set is pulled towards the opposite
end of the cell

Question 5

What is crossing over, and when does it occur in meiosis?

Answer 5

Crossing over is the exchange of genetic material between homologous chromosomes. It occurs during prophase I of meiosis.

Question 6

What are three (3) major differences between the daughter cells that are produced in mitosis
and the daughter cells that are produced in meiosis?

Answer 6

1. Number of Daughter Cells
2. Chromosome Number
3. Genetic Composition

Question 7

What is a karyotype?

Answer 7

A karyotype is an organized, visual representation of an individual’s complete set of chromosomes

Question 8

What is non-disjunction?

Answer 8

Non-disjunction is the failure of chromosomes to separate properly during cell division. This error can occur during either meiosis or mitosis.

Question 9

What is a trait?

Answer 9

A trait is a specific characteristic or feature of an organism that can be inherited, acquired, or influenced by environmental factors.

Question 10

What is an allele?

Answer 10

An allele is a specific version or variant of a gene.

Question 11

What does it mean when we say an allele is dominant? How about recessive?

Answer 11

A dominant allele is the version of a gene that is expressed in the phenotype (observable traits) even when only one copy is present (Aa)

A recessive allele is the version of a gene that is only expressed in the phenotype if two copies are present (homozygous recessive, (aa).

Question 12

What does homozygous mean in genetics? How about heterozygous?

Answer 12

An individual is homozygous for a gene if they have two identical alleles for that gene.

An individual is heterozygous for a gene if they have two different alleles for that gene.

Question 13

What is genotype?

Answer 13

A genotype refers to the genetic makeup of an organism, specifically the set of alleles it carries for a particular gene or set of genes.

Question 14

What is phenotype?

Answer 14

A phenotype is the observable physical or behavioral characteristics of an organism, which result from the interaction of its genotype (genetic makeup) and the environment. (eye-color)

Question 15

What is meant by homologous chromosomes?

Answer 15

Homologous chromosomes are pairs of chromosomes with the same structure, size, and genetic (positions of genes).

• Same Genes, Different Alleles:
• One from Each Parent:

Question 16

A man has six fingers on each hand and six toes on each foot. This is a dominant inherited trait. His wife and daughter each have the normal number of fingers and toes. What percent of their future children would you predict would have six fingers and toes? (Show
the Punnett square.)

Answer 16

Case 1: Man is FF (homozygous dominant). All of the children will inherit one F allele from the father and one f allele from the mother, so they will all be Ff.
100% of the children will have six fingers and toes (since the dominant allele F is present).

Case 2: Man is Ff (heterozygous). 50% of the children will be Ff (having six fingers and toes). 50% of the children will be ff (having the normal number of fingers and toes).

Question 17

Alkaptonuria is a metabolic disorder in which affected persons produce black urine. Alkaptonuria results from an allele (a) that is recessive to the allele for normal urine (A). Sally has normal urine, but her brother has alkaptonuria. Sally’s father has alkaptonuria, and her mother has normal urine. Give the genotypes for: Sally, her mother. her father, and her brother.

Answer 17

Sally: Aa (normal urine, carrier of the recessive allele)
Mother: Aa (normal urine, carrier of the recessive allele)
Father: aa (alkaptonuria)
Brother: aa (alkaptonuria)

Question 18

Mary had a baby daughter. Unfortunately, she is not sure who the father is. If you know that
Mary is blood type A, and her baby is blood type A, what can you conclude about the father’s
blood type?

Answer 18

The father’s blood type could be A, AB, or O

Question 19

What is the difference between incomplete dominance and codominance?

Answer 19

In incomplete dominance, neither allele is completely dominant over the other.

In codominance results in both alleles being fully and equally expressed in the phenotype.

Question 20

Polygenic inheritance and multiple alleles are both non-Mendelian patterns of inheritance.
Explain how they are different

Answer 20

Polygenic inheritance involves multiple genes contributing to a single trait and leads to continuous variation in the phenotype.

Multiple alleles refer to a situation where there are more than two alleles for a single gene, leading to multiple distinct phenotypes.

Question 21

Color deficiency is a recessive sex-linked genetic trait. If a man is color deficient, from which of
his parents did he receive the gene? Explain why.

Answer 21

The man must have inherited the color deficiency gene from his mother.

Since the mother has two X chromosomes, she can either have one normal X and one defective X (making her a carrier) or two defective X chromosomes (making her color deficient).

Question 22

Color blindness in humans is a sex-linked trait. Use a Punnett square to show the expected
genotypes and phenotypes of the children of a woman who is color blind and a man with normal
color vision.

Answer 22

Mother: XbXb
Father: XB (fathers x), Y(fathers y )
Daughters will be normal color vision but carriers (genotype XBXb).
Sons will be color blind (genotype Xb Y).
Expected Genotypes and Phenotypes:
50% chance of color-blind sons (Xb Y)
50% chance of carrier daughters with normal color vision (XB Xb)