Genetics

Question 1

1. Alleles
2. Genotype
3. Haplotype
4. Locus

Answer 1

1. Different sequences that may exist at a difference locus
2. Two alleles that are present in an individual at a given locus. Heterozygous means two different alleles are present. Homozygous means they are the same allele.
3. A linear order of closely linked alleles usually inherited as a unit.
4. Specific location or map position of a gene or marker.

Question 2

1. Meiosis

How many rounds of replication and division are involved?

When do homologous chromosomes pair?

What is the result?

Answer 2

One round of replication followed by two rounds of division.

Meiosis 1= maternal and paternal chromosomes pair. the only time that replicated homologous chromosomes come together and pair.

**This is where recombination Occurs**

RESULT= two 1N gametes

Question 3

Chromatid.

Describe pre-replication?

Describe post replication?

What is the final product?

Answer 3

Pre replication (G1) chromosome in one linear stranded DNA molecule.

Post replication each product of replication is a chromatid, joined by a single centromere to form a single chromosome.

Two sister chromatids are the identical products of one round of reolication

Question 4

1. Diploid
2. Haploid

Answer 4

1. (2n = 46) chromosomes. Diploid Chromosome content is 2C
2. (1n = 23) chromosomes. Haploid chromosome content is 1C

**During Mitosis or Meiosis the Cromosome content will be 4C

Question 5

Mitosis

How many rounds of replication and division take place?

What type of tissue does this take place in?

What is the result?

Answer 5

One diploid cell going through one round of replication and one round of division

Somatic Tissue

2 diploid daugher cells

Question 6

Independent Assortment

Answer 6

Unlinked Loci are transmitted independently during mitosis and meiosis.

Question 7

Describe Segregation in meiotic and mitotic divisions.

Answer 7

Genes occure in pairs, with equal chance for each allele to be transmitted to the offspring.

Question 8

Recombination

1. What is recombination and when does it happen?
2. What deterimines the probability of 2 loci crossing over
3. What forms between the sister chromatids
4. What advantage does it offer the species

Answer 8

1. Physical exchange of sister chromatids during the pairing of homologous chromosomes. Occurs in Prophase 1
2. Probability is a funcion of distance, further away is less likely. Cell has 46 croms and 23 homologous pairs. One to two corssovers per homologous pairs.
3. Chiasma forms at the site of crossing over.
4. Increases genetic diversity

Question 9

What is linkage?

What is linkage disequlibrium and what does it result in ?

Answer 9

1. Close relation of loci on the same chromosome
2. Co-occurance of alleles on the same chromosome more often than by chance. Over reprentation of specific haplotypes

Question 10

Independent Assortment

1.Describe the results of meiosis for

Loci A & B

2. Describe independent assortment for Loci A & D.

Answer 10

1. Loci A and B are unlinked and on separate chromosomes therefore gametes AB, Ab, aB, ab. will be of equal probability
2. Loci A and D are on the same chromosome but are far enough apart to be unlinked. Therefore we have the equal probability to get gamete, AD Ad aD ad.

Question 11

1. Describe the gametes formed for Loci A and E

Answer 11

1. Loci A and E are linked due to the proximity of the two loci. They will produce AE and ae 90% of the time. Very rarely will you get crossing over at loci this closely related.

Question 12

Describe the linkage disequlibrium for HAPLOTYPE A1A2 or a1a2.

Answer 12

There is very tight linkage between loci of the same haplotype and VERY rarely will they be separated. In this case the gamemes will be A1A2 or a1a2.

Question 13

What is a haplotype block and how will it affect independent assortment?

Answer 13

A haplotype of gene loci that occure between two recombination hotspotes in the genone will assort together.

Question 14

What differentiated femail gametogenesis from male gametogensis?

Answer 14

One primary Oocyte that enters meiosis will yield one mature gamete and three polar bodies.

Meiosis 1 and Meiosis 2 are both asymmetrical divisions.

Question 15

What is the progression of a mature gamete in the male meiosis?

Answer 15

1. Spermatagonium undergo mitotic expansion
2. Primary spermatocytes (2n) enter meiosis 1
3. Secondary spermatocytes (2n) enter Meiosis 2 and yield 4 (1n) spermatids
4. Spermatids (1n) mature into 4 mature spermatazoa

Question 16

When does male meiosis begin? How long does it continue?

Are any cells constantly active?

Answer 16

Puberty, continues throughout life

Yes there is a meiotic pool that is constantly dividing and offers many opportunities for mutation.

Question 17

What phase are germ cells arrested in during femail meiosis?

Answer 17

Prophase 1

Question 18

At Ovulation what happens to the arrested ooycyte? At what rate are they released?

Do women ever run out of germ cells?

Answer 18

Each oocyte resumes meiosis at the time of ovulation. This presents an age related risk of abnormal chromosome segregtation .

One Per month

Yes at menopause there will be a depletion of oocytes.

Question 19

What is an evolutionary result of linkage disequlibrium?

Answer 19

Linkage disequlibrium allows haplotype to be evolutionary conserved. Since the genes are in such close proximity they are rarely distributed during recombination.

Question 20

What is nondisjunction and when does it occure?

Answer 20

An error in chromosome segregation leading to an abnormal chromosome number in one or more daughter cells.

May occur in either mitosis or meiosis.

Question 21

What are some of the results of nondisjunction?

Name 2

When can they occure?

Answer 21

1. Missing Chromosome- results in a monosomy (n=45)
2. Extra chromosome- results in a trisomy (n=46)

**They can occure at any time in the cell cycle. **

Question 22

How many chromosomes are typically involved in nondisjunction?

When are women at the greatest risk?

Answer 22

You typically have a nondisjunction event in one chromosome and have 22 normal pairs.

Meiosis 1 and the risk increases exponentially with age

Question 23

Describe the mutation trend with age for men?

Describe the mutation trend for females?

Answer 23

1. As paternal age increases there are increasing number of mutation transmitted in the germ line. 20 year old father = 25 new mutations, 40 year old father = 65 new mutations.
2. Mothers contribute 14 mutations regardless of age.

Question 24

What is a mosaicism?

Answer 24

The presence of two (or more) geneitcally distinct cell lines within one individual

Question 25

When do mosaicisims arise?

Answer 25

Mosaicism may result when a genetic change arises in a cell undergoing MITOSIS

Question 26

Are mosaicisms pre-zygotic or post-zygotic?

Answer 26

The zygote is a single cell. By definition, when mosaicism is present, it must have arisen post-zygotically

Question 27

What causes Mosaicisms?

Answer 27

Any type of gene?c error may give rise to mosaicism – Nondisjunc?on → chromosomal mosaicism – New muta?on → gene?c mosaicism

Question 28

How are Mosaicisms distributed throughout the body?

Answer 28

Mosaicism: distribu?on of the abnormal cell line varies depending on site and ?ming of the error • Each case is unique → clinically unpredictable • Extra-embryonic vs. Embryonic (soma?c vs. germline)

Question 29

Which mutations are inheritable, somatic or germ line?

Answer 29

Germ line mutations are the only ones that can be inherited.

Question 30

What are some common features of Mosaicisms? Name 4

Answer 30

1. Typically, mosaicism involves a **normal cell line** and an **abnormal cell line** 2. The abnormal line is the consequence of a new mutation or nondisjunction occurring during **mitosis** 3. Each case is unique → clinically unpredictable 4. Extra-embryonic vs. Embryonic (somatic vs. germline)

Question 31

What is a result of a germ line mutation?

Answer 31

Can cause a family cancer syndrome or another example of genetic disease

Question 32

Consider two independent (unlinked) loci, either on two different chromosomes or far apart on the same chromosome. In an individual who is heterozygous at both loci, how many different gametes can be produced?

Answer 32

4

Question 33

DIV An individual is heterozygous at three loci (Aa,Bb,Dd). If alleles at these loci are in tight linkage disequilibrium, how many different gametes are predicted?

Answer 33

2

Question 34

DIV Which option provides the best summary of the genetic content of cells at the end of meiosis I?

Answer 34

Homologous chromosomes have separated

Question 35

DIV For pregnancies at high risk to be affected with a particular genetic disease, preimplantation diagnosis may be an option. In one approach, polar body biopsy is performed, and the first polar body is used for genotyping. For a mother who is heterozygous for a deleterious mutation, which option is consistent with an unaffected pregnancy?

Answer 35

The first polar body has two copies of the mutant allele.

Question 36

Track the alleles of a single locus through meiosis. In a person who is heterozygous (Aa), how many alleles and which alleles will be present in the daughter cells at the completion of meiosis I? Assume no recombination.

Answer 36

Cell 1=AA and Cell 2=aa

Question 37

ND At a locus on chromosome 21, a woman is heterozygous 1,2, and her husband is homozygous 1,1. Nondisjunction in maternal meiosis 1 would give rise to a child with trisomy 21 and what genotype? | (1 point)

Answer 37

1,1,2

Question 38

Pairing of Homologous Chromosomes only occurs in Mitosis, meiosis, or both?

Answer 38

Homologous Chromosomes only pair during Meiosis.

Question 39

Why do women have an increased risk of nondisjunction with age?

Answer 39

As the Oocyte spends more time arrested in prophase 1 there is a higher risk of mutation.