Human Genetics Exam 1

Heredity

the passing of traits from one generation to another

Genetics

the study of how traits and their variants are passed from parents to offspring in the form of genes

Gene

a functional unit of heredity. found in discrete DNA segment that encodes a functional product.

Genome

a whole set of genes (in nucleus, mitochondria and chromosomes)

Locus/loci

a particular position on a chromosome

Alleles

2 different version of the same gene

Mutation/ Variant

changes the alleles and how they arise (change of DNA sequence)

Genotype

genetic makeup of an organism… types of alleles

Phenotype

physical traits of a gene

Human gene nomenclature

all in caps + italicized in human genes

The central dogma of molecular biology describes what?

the expression of heredity information

How does one genome make all the cells in our body?

through cell specific gene expression

Basis for evolution

variation/ polymorphism

Somatic cells

all cells except germ cells, diploid, 46 total chromosomes (44 autosomes and 2 sex chromosomes)

Germ cells

gametes/ reproductive cells, 23 chromosomes (22 autosomes and X or Y sex chromosome)

Cell division

mitosis

cell death

apoptosis

Syndactyly

failure to sep digits in the womb due to no cell death

Phases of the cell cycle

G1, S, G2, prophases, pro metaphase, metaphase, anaphase, telophase, then G0 if needed

When do chromosomes replicate?

S phase

karyokinesis

nuclear separation

Outcomes of meiosis

4 genetically distinct haploid daughter cells, essential for life, makes genetic diversity

Meiosis 1 is a reductive division, why?

go from 46-23 chromosomes

When does crossing over occur?

in prophase 1 of meiosis

Synapsis

paring of homologous chromosomes

crossing over

exchange of genetic info

bivalent

chromosome pair

chiasma

place where recombination occurs

Why is meiosis 2 an equatorial division?

no DNA replication, 23 to 23 chormosomes

Do X and Y chromosnes undergo recombination?

yes, at the psuedoautosomal regions (the ends)

Gregor Mendel: the father of modern genetics

monk and scientist, 2 laws of inheritance, originally published work in 1866, was rediscovered in 1901

Self fertilization

pollen and egg from same plant

Cross-fertilization

artificially fertilized, fertilize eggs with pollen from different plants

Monohybrid cross

tracks inheritance pattern of a single trait

Phenotypic ratio of a monohybrid cross

3:1

Mendel’s first Law: The Law of segregation

during gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene

True Breeding

homozygous dominant or recessive

Test cross

a way to determine the genotype of something by crossing it with a pure breeding recessive

Genetically males are

XY and are hemizygours, and the recessive X allele is not masked

Genetically females are

XX and can be homozygous or heterozygous for a sex linked trait

How is mitochondrial DNA inherited

through the egg from the mother

Dihybrids

tracks inheritance of 2 traits simultaneously

Phenotypic ratio of a dihybrid cross

9:3:3:1

The product rule

the probability of simultaneous independent events equal the product of their individual probabilities

Mendel’s Second Law: The Law of Independent Assortment

During gamete formation, the segregation of alleles of one gene is independent of the segregation of alleles of another gene

Chi-Square test

statistical test to determine whether the difference between an observed and expected outcome of an experiment is statistically significant

Pedigree

family tree of inheritance, is useful for investigating the pattern of inheritance of a phenotype whose presence or absence is determined by the genotype at a single locus

First degree relatives

share 50% of genetic info with proband- parents, siblings, and children

Second degree relatives

share 25% of genetic info with proband- half-siblings, aunts, uncles, grandparents, nieces and nephews

Third degree relatives

share 12.5% of genetic info- first cousins

Mitochondiral inheritance

maternal inheritance, severity of symptoms can vary ( if mother is affected children will be/ if father is affected chiildren won’t be)

Autosomal Recessive inheritance

appears in both sexes equally, skips generations, affected offspring born to unaffected parents, when parents are hetero ~1/4 of the offspring will be affected

Autosomal Dominant inheritance

appears in both sexes equally, both sexes transmit the trait to offspring, doesn't skip generations, affected offspring must have an affected parents, unless they have a mutation, when parent is affected (hetero) and the other not ~ ½ the offspring will be affected, unaffected parents don’t transmit the trait

X-linked Recessive inheritance

more males than females affected, affected sons born to unaffected mothers; thus the trait skips a generation, a carrier mother makes ½ affected sons, all daughters of affected fathers are carriers

X-linked Dominant inheritance

both males and females affects, often more females, doesn’t skip generations, affected sons must have affected mother, affected daughters must have either affected mother or father, affected mothers if hetero will pass the trait to ½ of their sons and daughters

Y-linked inheritance

only males are affected, passed from father to son, doesn’t skip generations

Sum Rule

the probability of either of two mutually exclusive events occurring is the sum of their individual probabilities

Haplosufficient

the wild type allele supports wild type function in heterozygotes, Wild type allele is dominant, mutant allele is recessive

Haploinsufficient

wildtype allele does NOT support wild type function in heterozygotes, wild type allele is recessive, mutant allele is dominant

What are the functional consequences of mutation?

loss of function mutations and gain of function mutations

Null/ amorphic mutation

loss of function mutation, null alleles produce no functional product

Leaky/ hypomorphic mutation

loss of function mutation, leaky mutant allele produce a small amount of wild-type gene product

Dominant negative mutation

loss of function mutation (spoiler effect), the formation of multimeric proteins is altered by dominant negative mutants whose products interact abnormally with the protein products of other genes, leading to malformed multimeric proteins

Hypermorphic mutation

gain of function mutation, excessive expression of the gene product leads to excessive gene action.

Neomorphic mutation

gain of function mutation, the mutant allele has novel function that produces a mutant phenotype in homozygous and heterozygous organisms.

Incomplete Dominance

heterozygote phenotype is an intermediate level between the two homzygotes, no dominant or recessive allele (pink flowers)

Codominance

Heterozygote phenotype shows expression of both allele, AB blood type

Multiple Allels

a gene can have more that 2 alleles, different allele combos may produce variations in the phenotype, i.e fur color of rabbits

Lethal Alleles

genotype that causes death before an individual can reproduce, one expected genotype not observed in offspring (they are dead)

Sex-limited traits

have sex dependent phenotype, autosomal linked or X linked genera, hormone level differences, i.e beard growth, lactation

Sex-Influences traits

have variable inheritance patterns between sexes, alleles are dominant in one sex, recessive in another, again autosomal linked or X linked, hormone level difference, i.e pattern baldness, beards in goats

Phenocopy

is a phenomenon in which a trait appears to be inherited, but is caused by the environment, is not due to genotype, exposure to teratogens and infection

Pleiotropic

a gene that affects more than one trait, i.e Marfan syndrome (long limbs, caved-in chest, weakened aorta, lens dislocation)

Gene-environment

interactions that can also influence phenotype, i.e phenylketonuria, environment can be controlled by having a LOW diet of phenylalanine

Variable pentrance

all or none expression of a phenotype (polydactyly syndrome)

Variable expressivity

severity or extent of phenotype (waardenburg syndrome, hearing loss, different eye colors, white forelock, premature graying)

Cellular and organismal homeostasis requires what?

Many pathways, and mutations in any gene involved in the pathway can lead to altered phenotypes

Epistasis

the phenomenon of altered phenotypic rations due to gene interaction

No gene interaction

9:3:3:1 phenotypic ratio

Complementary gene interactions

9:7 phenotypic ratio, produced of both genes act in tandem in same pathway, both genes must have at least one wild type allele in order to have wild type phenotype

Complementation Analysis

distinguishes mutations in the same gene or different genes in a pathway

Complementation

parents have mutations in different alleles

Non-complementation

parents have mutations in the same gene

Duplicate gene action

15:1 phenotypic ratio, 2 genes encode products with redundant functions in a pathway, only need one dominant allele in either gene to produce wild type phenotype, homozygous recessive in both genes= mutant phenotype

Recessive Epistasis

9:3:4 phenotype, homozygous recessive genotype for one gene masks the genotype of another gene

Dominant Epistasis

12:3:1 phenotype, dominant allele in one gene masks the phenotypic expression of the allele in other gene

Syntenic genes

genes that are located on the same chromosome

Cis allele configuration

two dominant or two recessive alleles on each chromosome

Trans allele configuration

one dominant and one recessive allele on each chromosome

Genetic Linkage

genes that are closely spaced on the same chromosome are often inherited together

Linked genes

DO NOT assort independently UNLESS recombination occurs between them

What disrupts linkage?

recombination

Parental

(non-recombinant) have the parents allele configuration

Recombinant

(non-parental) have new combinations of alleles

Complete genetic linkage

genes extremely close together, no recombination between genes in F1 meiosis, gametes are all parental

Incomplete genetic linkage

recombination occasionally occurs between genes, more parental gametes than recombination gametes

Recombination frequency

number of recombinants/ total number, the smaller the value, the closer the genes are to each other

Two-point test cross

cross dihybrid to homozygous recessive

Genetic map

the probability genes will be separated by recombination

Physical map

distance between genes in base units