Lesson 16: Mendelian Genetics

Question 1

What is a gene?

Answer 1

Segment of DNA that (often) codes for a protein

Question 2

What is a trait?

Answer 2

Genetically determined characteristic or the expression of proteins

Question 3

What are alleles?

Answer 3

Alternate forms of a gene

Question 4

What is a phenotype?

Answer 4

Physical appearance of a trait (what it looks like)

Question 5

What is a genotype?

Answer 5

Genetic make up of a trait (the letters)

Question 6

What is a dominant allele?

Answer 6

Always expressed if present

Question 7

What is a recessive allele?

Answer 7

Only expressed if NO dominant allele is present

Question 8

What is a homozygous allele?

Answer 8

Two of the same alleles

Question 9

What is a heterozygous allele?

Answer 9

Two different alleles

Question 10

What is the P Generation?

Answer 10

Also known as the true breeding or parental generation. Always gonna be homozygous dominant or homozygous recessive for trait

Question 11

What is Mendels first law of genetics?

Answer 11

Law of dominance

Question 12

What does the law of dominance state?

Answer 12

An organism with a dominant allele will express the dominant trait and an organism with a recessive allele will ONLY have the trait expressed if the dominant allele is NOT present

Question 13

What is Mendels second law of genetics?

Answer 13

Law of segregation

Question 14

What is the law of segregation?

Answer 14

Each individual has two factors (alleles) for each trait. Alleles separate during the formation of gametes. Fertilization gives each new individual two alleles for each trait.

Question 15

What is Mendels third law?

Answer 15

Law of independent assortment

Question 16

What is the law of independent assortment?

Answer 16

Each pair of alleles segregated (assorts) independently of other traits in meiosis. The inheritance pattern of one trait will NOT affect the inheritance pattern of another. For a single human gamete, the possible ways for chromosomes to assort is an astounding 8,388,608 (2^23) possible combinations

Question 17

What does crossing over provide?

Answer 17

Additional variation. Crossing over produces entirely new combinations of alleles on a chromosome

Question 18

What is test cross?

Answer 18

Used to discover the unknown genotype of a known phenotype (the dominant phenotype). Cross a true-breeding recessive individual (yy) with a dominant phenotype (Yy or YY). Ratio reveals the unknown genotype. If ANY with the recessive trait appear, unknown MUST be heterozygous

Question 19

What is a pedigree?

Answer 19

Inheritance can be traced using a pedigree

Question 20

How can you tell the difference between a dominant inheritance and recessive inheritance on a pedigree?

Answer 20

Dominant inheritance:
All affected individuals will have a parent who also has the trait (ex: huntingtons disease)

Recessive inheritance:
An affected individual can arise from 2 unaffected parents (ex: cystic fibrosis (CF) and Phenylketonuria (PKU))

Question 21

What are the 7 special cases in genetics that Mendel didn’t account for?

Answer 21

Multiple alleles, codominance, incomplete dominance, incomplete penetrance, pleiotropic effects, epistatic interactions, and polygenic inheritance

Question 22

What is multiple alleles/codominance?

Answer 22

Some traits have more than two alleles. In these cases, sometimes more than one allele can act as a dominant allele. BOTH dominant alleles show up (ex: ABO blood type)

Question 23

What is incomplete dominance?

Answer 23

Occurs when one allele is not completely dominant over another (ex: red flower + white flower= pink flower)

Question 24

What is incomplete penetrsnce?

Answer 24

Alleles have a “true” dominant/recessive relationship, but dominant doesn’t always determine the phenotype (ex: polydactyly- autosomal dominant, but not all who inherit the gene have additional fingers)

Question 25

What is pleiotropic effects?

Answer 25

A single mutant gene affects two or more distinct and seemingly unrelated traits (ex: sickle cell anemia)

Question 26

What are epistatic interactions?

Answer 26

The action of one gene overrides the actions of another gene

Question 27

What is polygenic inheritance?

Answer 27

A phenotype is determined by more than one gene (ex: height, skin color, eye color, hair color)

Question 28

Why are males more affected by X-linked traits?

Answer 28

Males are affected by X-linked traits much more frequently than females because if they inherit an X with the recessive disorder they will have the disorder and visa versa