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MCB Exam 1

Terms in this set (103)

monohybrid cross

mendel's principles

principle of segregation and principle of independent assortment

principle of segregation

- monohybrid crosses
- states that for any trait, each parent's pairing of genes (alleles) split and one gene passes from each parent to an offspring. Which particular gene in a pair gets passed on is completely up to chance.
- results from pairing and separation of homologous pairs
- each individual possesses 2 alleles that separate (segregate) from each other during meiosis/when gametes are formed

Principle of Independent Assortment

dihybrid cross
The Law of Independent Assortment states that different pairs of alleles are passed onto the offspring independently of each other. Therefore, inheritance of genes at one location in a genome does not influence the inheritance of genes at another location.
- each homologous pair aligns independently
- alleles at different loci segregate independently of one another

only one copy of allele needed for expression of the gene

two copies of allele needed for expression of the gene

x linked traits

genes located on the X chromosome

y linked traits

Genes on the y chromosome concerned with gender determination primarily
Only expressed in males

term used to describe organisms that produce offspring identical to themselves if allowed to self-pollinate (homozygous)

monohybrid cross

A cross between individuals that involves one pair of contrasting traits

The F2 phenotypic ratio of a monohybrid cross is

3:1, dominant: recessive

F2 genotypic ratio monohybrid cross

The F2 phenotypic ratio of Mendel's dihybrid cross is

9:3:3:1
9 show dominant for both
3 and 3 for one but not the other
1 shows recessive for both

find probability of each phenotype by branch diagram `

first do probabilities of getting each phenotype from first trait, then split each of those options into two other options and multiply probabilities (like the urn problem)

Fork-line/Branch method

cross between an organism with an unknown genotype and an organism with a recessive phenotype

Complex Multi-factorial Disease

- conditions caused by many contributing factors
- likely associated with the effects of multiple genes (polygenic) in combination with lifestyle and environmental factors
- no clear pattern of inheritance despite clustering in families

discontinuous traits

controlled by variation in one gene
all or nothing traits

continuous traits/quantitative traits

Continuous traits are those that can exist in a range (height, age, skin color, etc.) and determined by multiple alleles

examples of continuous/quantitative traits

Crop Yield
Some Plant Disease Resistances
Weight Gain in Animals
Fat Content of Meat
IQ
Learning Ability
Blood Pressure

example of continuous vs discontinuous traits

Mendel's flowers were either white or purple (discontinuous) while other flowers could range from being pure white to lavender to strong purple, etc. (continuous)

The formula that predicts the number of genotypes from the number of genes is

3 to the power n (n is the number of genes)

- cause death usually early in development
- alleles that are incompatible with life
- can alter phenotypic ratios because result in missing or dead genotypic classes
- can be dominant or recessive

simple mendelian inheritance

-Complete dominance (AA=Aa in phenotype)
-Both parent contribute equally
-Trait is controlled by one gene
-Inheritance is governed by Principles of Segregation and Independent Assortment
-However, most phenotypes do NOT exhibit patterns of simple mendelian inheritance

recessive lethal allele

= 2 copies required for death
- homozygous recessive is missing or dies
- example: cystic fibrosis, sickle cell anemia

dominant lethal allele

= 1 copy needed for death
- heterozygotes and homozygous dominant are missing or die
- example: Huntington's disease

example of phenomenon of lethal alleles in humans

incomplete dominance

heterozygote is intermediate
- ex: hypercholesterolemia

- heterozygote exhibits both phenotypes at the same time (not something in between)
- example: ABO blood groups
- monohybrid genotypic and phenotypic ratios are 1:2:1
- all three genotypes phenotypically distinct

multiple alleles for a single locus

genes on autosomes more readily expressed in one sex

genes on X and Y chromosomes

autosomal genes expressed only in one sex (e.g., ovarian cancer)

genetic heterogeneity

a phenomenon in which a single phenotype or genetic disorder may be caused by any one of a multiple number of alleles or non-allele (locus) mutations
- different gene loci producing apparently identical disorders

one gene hides/masks the effect of another gene at a different locus

genomic imprinting

genes whose expression is influenced by sex of transmitting parent

concept of dominance

= interaction between alleles at the same locus

one of a number of different forms of a gene

dominant allele

heterozygote is the same as one parent

example of codominance in humans

ABO blood types

gene interaction

genes at multiple loci determine a single phenotype

a single gene responsible for a variety of traits

example of pleiotropy in humans

cystic fibrosis

pseudoautosomal regions
- 5% of the chromosome
- contains genes shared with X chromosome

male specific region of the Y chromosome
- 95% of chromosome
- contains majority of genes including: SRY (stimulates male development) and AZF (required for sperm production)
- X and Y do not recombine over most of their lengths

sex determining region of the Y chromosome

polygenic trait

phenotypic outcome depends upon more than one gene

example of a human characteristic that displays epistasis

bombay phenotype

bombay phenotype

Homozygous recessive for a mutation which masks the genotype for blood groups

during a monohybrid cross, 1:2:1 phenotypic and genotypic ratios are found in what

incomplete dominance
codominance
additive alleles

percentage of individuals with a particular genotype that express the expected phenotype

incomplet penetrance

genotype does not produce expected phenotype

degree to which a character is expressed

example of incomplete penetrance and variable expressivity

human polydactyly

obstacles to study of characteristics in humans

1. no controlled matings
2. long generation time
3. small family size

how can we investigate characteristics in humans

1. pedigrees
2. twin studies
3. adoption studies

on a pedigree chart what shapes are female and male

circle female square male

mating between relatives on pedigree

mating between related individuals

three steps that we do in pedigree analysis to determine mode

1. dominant or recessive?
2. autosomal, sex-linked or mitochondrial?
3. confirm chosen mode of inheritance works for all individuals (write in the genotypes)

1. how do we know if it is dominant or recessive

dominant: affected individuals have at least one affected parent
recessive: affected individuals can be born from unaffected parents

people outside family (marrying in) are homozygous normal

if a trait is passed dad to son it is not

estimates the proportion of phenotypic variation in a population due to genetic differences. specific to a particular population at a particular time

100% of variation is genetic & no effect of environment

all variation is due to the environment

both twins share a trait

in concordance studies, for a completely heritable trait, MZ concordance and DZ concordance should be

1.0 for MZ and .5 to DZ

greater the difference between MZ and DZ concordance,

the greater the degree of genetic control

y-linked mode of inheritance

fathers pass the trait to all sons and only males are affected

only mothers pass trait to all children

x-linked dominant

affected fathers pass trait to all daughters
- trait never passed father --> son

x linked recessive

more males than females are affected
- daughters of affected fathers must be carriers
- affected mothers pass trait to all sons

blue diaper mistake

it's x linked recessive not autosomal

experiments that identify and describe the genetic material

1. griffith 1928
2. Avery Macleod and mcarty
3. Hershey and chase

experiments to solve the structure of DNA

1. Chargaff = ratio 1:1 of purines to pyrimidines
2. rosalind franklin = helical structure, phosphates are backbones
3. Watson & crick = covalent phosphodiester bonds between nucleotides, hydrogen bonds

Avery, MacLeod, McCarty

Determined that DNA was Griffith's "Transforming Factor." found what chemical thing it was

Hershey and chase

Used radioactive material to label DNA and protein; infected bacteria passed on DNA; helped prove that DNA is genetic material not proteins

three traits of hereditary material

1. chemical stability and genetic stability (faithful copies)
2. storage of great amounts of information
3. potential for change (mutation)

single building block = nucleotide

three parts of nucleic acid

1) phosphate group (PO4-3)
2) sugar
3) base

adenine and guanine (2 rings)

cytosine and thymine (1 ring)

How many hydrogen bonds are between A and T?

how many hydrogen bonds between g and c?

A virus that infects bacteria

how does the structure of DNA fulfill it's three functions

Complementary base-pairing between two strands allow each strand to serve as a template for synthesis of a new double-stranded DNA molecule
b) Over 3 billion base-pairs in human genome with a 3 letter code (triplet codons) DNA RNA Protein
c) A single nucleotide change may result in an amino acid change, leading to a potential change in the structure and function of a protein (aka trait)

An enzyme that untwists the double helix of DNA at the replication forks.

An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template.

A short segment of DNA that acts as the starting point for a new strand

Enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule

primer used for in vivo replication

DNA polymerase goes what direction

polymerase for pcr

A DNA synthesis enzyme that can withstand the high temperatures of PCR

bottom to top with shortest fragments on the bottom and then going up is the same as left to right on the colored graph, also bottom to top is 5-->3

temperatures of pcr

sequencing by synthesis

Determining the sequence of a large DNA molecule through the automated, stepwise synthesis of fluorescently tagged DNA using millions of small, overlapping, single-stranded DNA templates derived from that larger sequence.

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