Genetics- Mendel and Meiosis

Question 1

State the Composition of Eukaryotic chromosomes

Answer 1

DNA coiled and condensed around proteins called histones

Question 2

Define karyotyping

Answer 2

arrangement of chromosomes into homologous pairs

Question 3

Distinguish between autosomes and sex chromosomes

Answer 3

autosome: chromosome that is not a sex chromosome (#1 to #22)
sex chromosome: chromosome that originates from productive organs (#23)

Question 4

Describe the reduction division in terms of diploid and haploid numbers of chromosomes in meiosis

Answer 4

At the beginning of meiosis, the cell starts with a diploid, and at the end, 4 daughter cells are produced containing one haploid each

Question 5

define homologous chromosomes

Answer 5

a pair of chromosomes that have the same size, centromere position, and staining position

Question 6

Outline the process of meiosis

Answer 6

-Preceded by replication of chromosomes
-Single replication followed by two divisions
-Four daughter cells
-Each has HALF the chromosomes

Question 7

Explain the steps of meiosis

Answer 7

• Interphase I: chromosomes replicate and two sister chromatids are attached at the centromere
• Prophase I: Chromosomes condense, synapsis occurs (homologous chromosomes come together), tetrad (complex of four sister chromatids), chiasmata (where non-sister chromatids are linked)
• Metaphase I: Tetrads align at the metaphase
• Anaphase I: Homologous separate but Sister chromatids stay connected
  -Telophase I and Cytokinesis: Chromosomes reach opposite poles, cleavage furrows or cell plates divide the cell, and NO DNA replication occurs
• Prophase II: Spindle apparatus forms, chromosomes move toward the equator
• Metaphase II: Chromosomes align at the metaphase
• Anaphase II: Centromeres of sister chromatids separate
  Telophase II and Cytokinesis: Nuclei form at opposite ends of the cell, Cytokinesis occurs and produces 4 haploid daughter cells

Question 8

Explain how meiosis results in effectively infinite genetic variety in gametes through crossing over in prophase I, independent Assortment, and Random fertilization (FRQ)

Answer 8

• crossing over: the exchange of genetic material between homologous occurs during prophase of meiosis I. Two homologous portions of two non-sister chromatids trade places at chiasmata. Produces chromosomes w/ genes from both parents
  -independent Assortment: In metaphase I, the alignment of the homologous pair of chromosomes is random. 2^n possible combinations of chromosomes in gametes (n is haploid #)
  -Random Fertilization: Sperm has 1 in 8 mill. Possible combos.Totals zygote with 1 in 64 trillion possible diploid combos.

Question 9

Define gene, allele, and genome

Answer 9

-gene: units of hereditary info, made of DNA, on chromosomes
-allele: alternate forms of a gene
-genome: complete set of DNA (genetic material) in Organisms

Question 10

Define gene mutation

Answer 10

mutation: changes in genetic material
a new mutation in the gene may have an effect on some or all traits simultaneously

Question 11

What is a human pedigree?

Answer 11

-human pedigree: a family tree that shows the relationship among parents and children across generations
women: squares dominant: shaded
men: circles recessive: non-shaded

Question 12

State Mendel’s Law of Segregation

Answer 12

Mendel’s Law of Segregation: allele pairs separate during gamete formation, one from each parent is passed on to offspring

Question 13

Explain the relationship between Mendel’s Law of Segregation and Meiosis

Answer 13

The basis of Mendel’s Law of Segregation is the first division of meiosis (meiosis I) in which homologous chromosomes are separated

Question 14

Define genotype

Answer 14

genotype: an organism’s genetic makeup. (Ex. Tt or TT or tt)

Question 15

Define Phenotype

Answer 15

Phenotype : an organism’s expressed traits (Ex. tall or short)

Question 16

Define dominant allele

Answer 16

Dominant allele: an allele that will be expressed if it is present (represented by capital letters)

Question 17

Recessive allele

Answer 17

Recessive allele: an allele that will only expressed in the absence of a dominant allele (represented by lower-case letters)

Question 18

Define codominant alleles

Answer 18

Codominant alleles: Inheritance characterized by full expression of both alleles in heterozygote

Question 19

Define locus

Answer 19

Locus: specific location on a chromosome that contains a gene

Question 20

Define homozygous

Answer 20

Homozygous: two identical alleles for a trait (TT or tt)

Question 21

Define heterozygous

Answer 21

Heterozygous: two different alleles for a trait (Tt)

Question 22

Define carrier

Answer 22

Carrier: heterozygous that carry the recessive allele

Question 23

Describe the concept of incomplete dominance, multiple alleles, pleiotropy, and epistasis

Answer 23

-incomplete dominance: Dominant phenotype is not fully expressed, leading to intermediate dominance;
Does NOT support the blending theory
-multiple alleles: More than just two alternate forms of a gene (Ex. ABO blood group)
- pleiotropy: The ability of a single gene to have multiple phenotypic effects. Consequently, a new mutation in the gene may have an effect on some or all traits simultaneously
-epistasis: Interaction between two nonallelic genes in which one modifies the phenotypic expression of the other. These genes are sometimes called modifier genes.

Question 24

Define polygenic inheritance and give two examples of such inheritance

Answer 24

polygenic inheritance: Mode of inheritance in which the additive effect of two or more genes determines a single phenotypic character
Ex. Skin color, hair color

Question 25

Describe ABO blood groups as an example of codominance and multiple alleles (FRQ)

Answer 25

Codominance is when inheritance is characterized by the full expression of both alleles in heterozygotes. ABO blood type is possible because A and B are dominant to O. This means that blood group A can have either AA or AO and blood group B can have either BB or BO due to multiple alleles. ABO can appear in offspring because both A and B are dominant and want to fully express leading to codominance.

Question 26

State Mendel’s Law of Independent Assortment

Answer 26

Law of Independent Assortment: Each allele pair aligns on the metaphase plate independently of other gene pairs during gamete formation

Question 27

Explain Genetic Disorders: Cystic Fibrosis, Huntington’s Disease, Sickle-Cell Disease, and Tay-Sachs Disease

Answer 27

-Cystic Fibrosis – 1/2,500 Caucasians, chloride channels don’t function→ accumulate mucus in the pancreas, lungs, intestines
-Huntington’s Disease: 3 to 7/ 100,000 European ancestry, autosomal dominant, nerve cells in the brain break down over time
-Sickle-Cell Disease: 1 in every 400 African Americans born in the U.S., Single amino acid substitution in hemoglobin,1/10 are heterozygous, Increases resistance to malaria
- Tay-Sachs: 1/3,600 births: 100 times higher in Jewish people of European descent, Brain cells don’t metabolize lipids, child dies after a few years at most

Question 28

Compare & Contrast Meiosis and Mitosis (FRQ)

Answer 28

Meiosis:
1. is a reduction division
2. division of sex cells
3. produces 4 haploid daughter cells
4. each daughter cell is genetically different due to genetic variation
5. each daughter cell contains HALF on the chromosomes (23)
6. two successive cell divisions
Mitosis:
1. division of somatic cells
2. produces two diploid cells
3. cells are genetically identical
4. each new cell has a complete set of chromosomes (46 chromosomes)
5. only one cell division

Both
- DNA replication occurs once
-the creation of new cells
-begins with one parent cell