Mendels Experiments and Heredity

Question 1

Early Heredity

Answer 1

People knew that sperm and eggs
transmitted information about traits
Early on the “Blending theory” was
prevalent
Problem:
Would expect variation to disappear after
a while and all traits be the same a while and all traits be the same
Variation in traits persists or re-occurs in later generations

**this may be good or bad or have no
effect on the resulting offspring

Question 2

Alleles

Answer 2

All Genes occur as pairs
Some genes may have more than 2 alleles
(multiple alleles) present in the genome but you(multiple alleles) present in the genome but you
normally receive only 2.
Alleles are different molecular forms of the same gene
Homozygous
having two identical alleles at a locus
AA or aa
Heterozygous
having two different alleles at a locus.
AaAa

Question 3

Law of Dominance

Answer 3

Dominant allele masks a recessive allele
that is paired with it
The dominant allele is expressed with a
capital letter (T)
The recessive allele is expressed with a
lower case letter (t)

Question 4

Genotype /phenotype

Answer 4

Genotype refers to particular genes an
individual carries (genotype)
 Phenotype refers to an individual’s
observable traits (what you see)
 Cannot always determine genotype by
observing phenotype

Question 5

Tracking Generations

Answer 5

Parental generation mates to produce (P)
First- generation offspring mate to produce (F1)
Second-gen offspring (F2)

Question 6

Monohybrid

Answer 6

Experimental cross between
two F1 homozygotes comparing 1 trait.F2 plants showed dominant-to-recessive ratio that averaged 3:1

Question 7

Mendel’s Theory of Segregation

Answer 7

An individual inherits a unit of information (allele) about a trait from each parent

During gamete formation, the alleles segregate from each other independently

Question 8

Parts of a Monohybrid Punnett Square

Answer 8

Example: A cross between a parent pea that is homozygous dominant for plant height (TT) and a parent pea that is heterozygous for plant height (Tt). What would the resulting offspring genotypes and phenotypes be?

Key:
T = tall plants (TT or Tt)
t = short plants (tt)

Parental Genotype:
Dad = TT (dad can donate T or T) t
Mom = Tt (mom can donate T or t)

Genotype Ratio (GR) = 2 TT : 2 Tt
Phenotype Ratio (PR) = 4 tall plants
Individual that shows dominant phenotype (may be AA or Aa) is crossed with individual with recessive phenotype (aa)

Examining offspring allows you to determine the genotype of the dominant individual

Question 9

Independent Assortment

Answer 9

Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait. Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis

Question 10

ABO Bloodtyping

Answer 10

AA or AO = type A blood
BB or BO = type B blood
AB = type AB blood
OO = type O blood

Hint: A and B are co-dominant to each other but O is recessive to A and B
Recipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surface
Type O is universal donor because it has neither type A nor type B glycolipid which could lead to coagulation (clotting) of blood

Question 11

Pleiotropy

Answer 11

Alleles at a single locus may have effects on two or more traits

Marfan syndrome - Mutation in gene for fibrillin (a protein fiber) that affects skeleton, cardiovascular system, lungs, eyes, and skin

Question 12

Epistasis

Answer 12

Interaction between the products of gene pairs

One gene pair can over-ride the effects of another gene pair

Common among genes for hair color in mammals
controls comb shape in poultry

Question 14

Crossing Over

Answer 14

Each chromosome becomes zippered to its homologue
All four chromatids are closely aligned
Nonsister chromosomes exchange segmentsAfter crossing over, each chromosome contains both maternal and paternal segments
Genes cross over more when they are further apart
Creates new allele combinations in offspringGenes on one type of chromosome that are close together
Genes that are closely linked are less likely to separate during gamete formation
Not all genes on chromosome are tightly linked
Genes crossover more often when they are further apart

Question 15

Environmental Effects on Plant Phenotype

Answer 15

Hydrangea macrophylla – flower color is affected by soil pH

Flower color ranges from pink (6-7 pH) to blue (5.0-5.5 pH)
Rabbit is homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin-producing pathway
Melanin is produced in cooler areas of body to gather more sunlight energy to generate heat

Question 16

Some Traits Show No Variation

Answer 16

Some human traits occur as a few discrete types

Attached or detached earlobes

Widows peak or No Widows peak

Albinism

Many Genetic Disorders

A more or less continuous range of small differences in a given trait among individuals
hair, eye, and skin color (all due to melanin)
Height and weight
The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait