Biology 142 Midterm Exam 1 - Emory
University - Mendelian Genetics -
Learning Objectives
Define: wild-type - ANSWER-"normal" phenotype (most often to occur in the wild)
dominant allele - ANSWER-An allele whose trait always shows up in the organism when
the allele is present.
recessive allele - ANSWER-An allele that is hidden whenever the dominant allele is
present
Explain how a mutation can cause a phenotype given the function of a protein -
ANSWER-a mutation of a gene can lead to the synthesis of a protein that is different
from the wild type, or can lead to no protein synthesis at all. The former is the case with
"baby superman", who had a mutation that caused a lack of the protein myostatin
(protein that restrains muscle growth).
Describe Mendel's Law of Segregation - ANSWER-Each gamete receives one member
of a pair of alleles.
Example: an Aa individual makes gametes that are either "A" or "a"
Define: phenotype - ANSWER-physical characteristics of an organism
Define: genotype - ANSWER-genetic makeup of an organism
Define: allele - ANSWER-one of two or more alternative forms of a gene that arise by
mutation and are found at the same place on a chromosome
Define: homozygous - ANSWER-having two identical alleles of a gene
Define: heterozygous - ANSWER-having two different alleles of a gene
Describe Mendel's Law of Independent Assortment - ANSWER-Alleles of different
genes assort into gametes independently of each other.
Example: Ss and Yy will sort into gametes independent of each other
Use a test cross to determine if an individual is homozygous dominant or heterozygous
- ANSWER-Test cross: cross between a dominant trait individual with a homozygous
recessive can determine whether the individual with the dominant trait is heterozygous
, or homozygous. If the unknown is homozygous dominant, all the progeny will have the
dominant trait. If the unknown is heterozygous, half the progeny will have the dominant
trait and half will have the recessive.
Determine whether two genes are linked on the same chromosome or are unlinked
using a two-point test cross. - ANSWER-For a cross between BbVv x bbvv, we would
expect a 1:1:1:1 ratio, but that is not the case if the genes are linked. The frequency of
the parental phenotypes is much higher than the recombinant phenotypes.
Calculate the distance between two linked genes on a chromosome using a two-point
test cross - ANSWER-Distances between genes are measures in map units. One map
unit corresponds to a recombination frequency of 1%, and is also referred to as a
centimorgan (cM).
map units/recombination frequency= total number of recombinants divided by total
number of progeny multiplied by 100
Draw a simple genetic map based upon data from test crosses - ANSWER-(use the
map units to figure out the order of genes on the chromosome)
Explain the effect of partial or incomplete dominance of alleles on Medelian ratios. -
ANSWER-Incomplete dominance = "blending" of traits in the heterozygotes. For
example, RR(red) x WW(white) = all RW(pink) offspring in the F1. However, F2 progeny
will have a ratio of 1 red: 2 pink: 1 white, which opposes the "blending" theory.
Describe the effect of the co-dominance of alleles on Medelian ratios using human ABO
blood types as an example - ANSWER-Codominance = two different alleles for a gene
are both expressed in the heterozygotes at the same time.
Blood type example:
Two IA or IA and IO results in type A
Two IB or IB and IO results in type B
Two IO results in type O
IA and IB results in blood type AB. These alleles are codominant.
Explain the basic conventions of probability - ANSWER-If an event is certain, prob = 1
If an event cannot happen, prob = 0
Otherwise somewhere in between
solve genetics problems using the Rule of Multiplication and the Rule of Addition to
determine the probability of expected genotypes and phenotypes - ANSWER-Rule of
Multiplication:
To determine the probability that two independent events will both happen...the general
rule is to multiply the probabilities of the individual events.
Rule of Addition:
The probability of an event that can occur in two or more different ways is the sum of
the individual probabilities of those ways
University - Mendelian Genetics -
Learning Objectives
Define: wild-type - ANSWER-"normal" phenotype (most often to occur in the wild)
dominant allele - ANSWER-An allele whose trait always shows up in the organism when
the allele is present.
recessive allele - ANSWER-An allele that is hidden whenever the dominant allele is
present
Explain how a mutation can cause a phenotype given the function of a protein -
ANSWER-a mutation of a gene can lead to the synthesis of a protein that is different
from the wild type, or can lead to no protein synthesis at all. The former is the case with
"baby superman", who had a mutation that caused a lack of the protein myostatin
(protein that restrains muscle growth).
Describe Mendel's Law of Segregation - ANSWER-Each gamete receives one member
of a pair of alleles.
Example: an Aa individual makes gametes that are either "A" or "a"
Define: phenotype - ANSWER-physical characteristics of an organism
Define: genotype - ANSWER-genetic makeup of an organism
Define: allele - ANSWER-one of two or more alternative forms of a gene that arise by
mutation and are found at the same place on a chromosome
Define: homozygous - ANSWER-having two identical alleles of a gene
Define: heterozygous - ANSWER-having two different alleles of a gene
Describe Mendel's Law of Independent Assortment - ANSWER-Alleles of different
genes assort into gametes independently of each other.
Example: Ss and Yy will sort into gametes independent of each other
Use a test cross to determine if an individual is homozygous dominant or heterozygous
- ANSWER-Test cross: cross between a dominant trait individual with a homozygous
recessive can determine whether the individual with the dominant trait is heterozygous
, or homozygous. If the unknown is homozygous dominant, all the progeny will have the
dominant trait. If the unknown is heterozygous, half the progeny will have the dominant
trait and half will have the recessive.
Determine whether two genes are linked on the same chromosome or are unlinked
using a two-point test cross. - ANSWER-For a cross between BbVv x bbvv, we would
expect a 1:1:1:1 ratio, but that is not the case if the genes are linked. The frequency of
the parental phenotypes is much higher than the recombinant phenotypes.
Calculate the distance between two linked genes on a chromosome using a two-point
test cross - ANSWER-Distances between genes are measures in map units. One map
unit corresponds to a recombination frequency of 1%, and is also referred to as a
centimorgan (cM).
map units/recombination frequency= total number of recombinants divided by total
number of progeny multiplied by 100
Draw a simple genetic map based upon data from test crosses - ANSWER-(use the
map units to figure out the order of genes on the chromosome)
Explain the effect of partial or incomplete dominance of alleles on Medelian ratios. -
ANSWER-Incomplete dominance = "blending" of traits in the heterozygotes. For
example, RR(red) x WW(white) = all RW(pink) offspring in the F1. However, F2 progeny
will have a ratio of 1 red: 2 pink: 1 white, which opposes the "blending" theory.
Describe the effect of the co-dominance of alleles on Medelian ratios using human ABO
blood types as an example - ANSWER-Codominance = two different alleles for a gene
are both expressed in the heterozygotes at the same time.
Blood type example:
Two IA or IA and IO results in type A
Two IB or IB and IO results in type B
Two IO results in type O
IA and IB results in blood type AB. These alleles are codominant.
Explain the basic conventions of probability - ANSWER-If an event is certain, prob = 1
If an event cannot happen, prob = 0
Otherwise somewhere in between
solve genetics problems using the Rule of Multiplication and the Rule of Addition to
determine the probability of expected genotypes and phenotypes - ANSWER-Rule of
Multiplication:
To determine the probability that two independent events will both happen...the general
rule is to multiply the probabilities of the individual events.
Rule of Addition:
The probability of an event that can occur in two or more different ways is the sum of
the individual probabilities of those ways
