Chapter 19 Medelian Genetics

Question 1

Law of Segregation

Answer 1

When gametes are made, the two traits carried by each parent separate.
Parent = Aa
Gamete = (A) (a)

Question 2

Law of Dominance

Answer 2

Dominant gene over recessive

AA crossed with aa only expresses dominant trait.

Question 3

Law of Independent Assortment

Answer 3

Genes located on different chromosomes assort independently of each other.

Question 4

Monohybrid Cross

Answer 4

Tt x Tt = ?
1 : 2: 1 genotype ratio
TT: Tt: tt
Phenotype ratio 3:1 Tall:short

Question 5

Testcross or backcross

Answer 5

Used to find out if it’s homozygous or heterozygous.
Cross it with homozygous recessive individual.
If we get all same trait the original is homozygous dominant.
If we get a mixed then the original was heterzygous.

Question 6

Dihybrid Cross

Answer 6

Cross between individuals with two genes.
AaBb.
9:3:3:1 phenotypic ratio F2 generation

Question 7

Incomplete Dominance

Answer 7

Blended phenotype, neither of the two alleles exerts dominance.

Question 8

Codominance

Answer 8

Both expressed at the same time.

E.g. AB blood types.

Question 9

Epistatic Genes

Answer 9

A gene that covers up the expression of another gene in the phenotype.

Question 10

Pleiotropy

Answer 10

occurs when one gene influences two or more seemingly unrelated phenotypic traits.

Question 11

Can two heterozygotes give a 2:1 ratio in a Punnett Square?

Answer 11

Yes, if there is a lethal gene. Only AA and 2 Aa.

Question 12

Polygenic inheritance

Answer 12

Two or more genes contributing to a single trait.

Question 13

Multiple Alleles

Answer 13

When a gene has more than two given alleles.

ABO blood type.

Question 14

When the wrong blood type is given

Answer 14

Clumping or agglutination would occur to cleanse the blood to foreign protein.

Question 15

Y linked traits

Answer 15

Holandric inheritance

Question 16

X link diseases examples

Answer 16

1) Colour blindness
2) Hemopgilia
3) Duchenne Muscular Dystrophy

Question 17

Barr Body

Answer 17

1 chromosomes inactivated in the embryonic development by methylation

Question 18

Autosomal recessive inheritance

Answer 18

Autosomal = non sex linked chromosome
E.g. Cystic fibrosis: Defect in Cl- channel protein, excessive mucus with infections.
Albinism: Absense of melanin
PKU: Unable to metabolize phenylalanine
Affects both sexes equally, can appear to skip generations.

Question 19

Autosomal Dominant Inheritance

Answer 19

No sex preference, no skipping gens, if you have one affected gene, you have the disease.
E.g Achondroplasia (dwarfism) and Marfan Syndrome (Connective tissue disorder).

Question 20

2 people heterozygous for an autosomal dominant disorder

Answer 20

Phenotypic ratio 3:1
Genotype ratio 3:1
AA and Aa have the disease

Question 21

Males give x linked genes to only their ____

Answer 21

Daughters, not sons

Question 22

A male gets a sex linked disease from his

Answer 22

Mother

Question 23

Pedigree tips

Answer 23

Determine whether the trait is dominant or recessive: If the trait is dominant, one of the parents must have the trait.
Determine if the chart shows an autosomal or sex-linked (usually X-linked) trait:For example, in X-linked recessive traits, males are much more commonly affected than females. In autosomal traits, both males and females are equally likely to be affected (usually in equal proportions).

Question 24

Linkage and Crossing Over

Answer 24

Linkage could be disrupted when crossing over occurs during meiosis.
The farther apart two genes are on a chromosome, the greater the frequency of crossover and recombination between them.

Question 25

Chromosomal Abnormalities

Answer 25

Nondisjunction, failure of homologous chromosomes to separate in Anaphase I or II of meiosis.
Wrong number of chromosomes, called aneuploidy.

Question 26

Chromosomal abnormalities example

Answer 26

Turner syndrome, Kleinfelter syndrome, down syndrome

Question 27

Turner Syndrome

Answer 27

Female with 1 X chromosome, no bar bodies in this sterile female. Only viable monosomy known in humans.

Question 28

Kleinfelter Syndrome

Answer 28

A male with XXY, sterile male with feminization

Question 29

Down syndrome

Answer 29

Extra 21 chromosome, trisomy 21, mental retardation, heart defects, more prone to Alzheimers and Leukemia

Question 30

Polyploidy

Answer 30

Common in plants (weeds, danelions, and wild oats). 3N or 4N cells. Endosperm of plant seeds are 3N. Human liver cells can be 3N or 4N.

Question 31

Deletion

Answer 31

Missing gene due to break or fragment lost. Chromosomal deletions are associated with some cancers.
Cri du chat syndrome: short arm of chromosome #5 is deleted.

Question 32

Duplications

Answer 32

Addition is now added on a chromosome from one that is fragmented. Partial Trisomy results. Radiation, chemicals, or even viruses.

Question 33

Translocation

Answer 33

Deleted chromosome fragment is joined to a nonhomologous chromosome.
Robertsonian translocation - chromosome 21 long arm onto the long arm of chromo 14.

Question 34

Amniocentesis

Answer 34

Amniotic fluid of the fetus can be cultured and subjected for karytopic analysis. Fetal secretions and epidermal cells from respiratory and GI tract.

Question 35

Ultrasound

Answer 35

Fetus is visualized to see any morphological defects prenatally.

Question 36

CVS (Chorion Villus Sampling)

Answer 36

Sample of placenta is removed. Higher risk than amniocentesis.
How many gametes can be made given the following genotype? Xx Yy Zz WW BB
2n rule, n= number of heterozygotes