Heredity Flashcards
Homologous pairs?
- 2 different copies of the same chromosome in a diploid organism
- 1 from each parent
Penetrance?
Proportion of individuals who have the phenotype associated with a specific allele
Incomplete dominance?
When one allele is not completely expressed over its paired allele. (R x W= Pink)
Codominance
when the heterozygous genotype expresses both alleles. (Ex. red x white = red + white spots).
Pleiotropy
when one gene is responsible for many traits
- single gene has multiple phenotypic outcomes
Polygenic inheritance
when many genes are responsible for one trait
- multiple genotypes are affecting one phenotype
Haploinsufficiency
1 copy of the gene is lost/ nonfunct. and the expression of the remaining copy is not sufficient enough to result in a normal phenotype
What organelle contains DNA that only comes from our maternal side?
mitochondria
Proto-oncogenes
are genes that can become oncogenes (cancer-causing genes) due to gain-of-function mutations. Cancerous growth occurs as a result
- Normally involved in cell cycle control.
- Follow 1 hit hypothesis
Gain-of-function mutations?
Causes too much protein to be made or production of an over-active protein
One hit hypothesis?
A gain-of-function mutation in one copy of the gene turns it into an oncogene.
Tumor-suppressor genes?
- Genes that become cancerous as a result of loss-of-function mutations
- Normally needed to suppress cancerous growth.
- follow the two hit hypothesis
- Are haplosufficient
- Have null alleles when they become cancer-causing.
Two hit hypothesis?
A loss-of-function mutation in both copies of the gene are needed to make it cause cancer.
Null alleles?
From mutations that cause the alleles to lack normal function. Tumor-suppressor genes have null alleles when they become cancer-causing.
What are the 3 important tumor-suppressing genes?
p53
p21
RB gene
p53 is what?
-Tumor-suppressor gene
- Guardian of the cell
- Upregulated to prevent cells from becoming cancerous
p21 is what?
- Tumor-suppressor gene
- Inhibits phosphorylation activity in order to decrease rampant cell division.
Retinoblastoma gene (RB) is what?
- Tumor-suppressor gene
- Codes for a retinoblastoma protein
- Prevents excessive cell growth during interphase.
Nondisjunction is what?
What are the types of this?
- Improper segregation of chromosome pairs during anaphase
- Produces daughter cells with an incorrect # of chromosomes
- Two types: one occurs in Meiosis 1, another occurs in Meiosis 2
Single nondisjunction of homologous chromosomes during meiosis I #’s
2n+1, 2n+1, 2n-1, 2n-1
Single nondisjunction of homologous chromosomes during meiosis 2 #’s
2n, 2n, 2n+1, 2n-1
- only one side is affected
Single nondisjunction of sister chromatids during mitosis #’s
2n+1, 2n-1
Aneuploidy
Abnormal # of chromosomes in the daughter cells
Trisomy
3 chromosome copies (or 1 extra copy)
Monosomy
1 chromosome copies (1 missing copy)
Disomy
Refers to a normal diploid cell.
Down syndrome
Trisomy of chromosome #21 (each diploid cell has 47 chromosomes total).
Turner syndrome
Monosomy of X chromosome in females (each diploid cell has 45 chromosomes total).
Klinefelter’s syndrome
Trisomy of X in males
Giving them XXY (each diploid cell has 47 chromosomes total)
Trisomy X
Trisomy of X in females
Giving them XXX (each diploid cell has 47 chromosomes total)
True-breeding?
- Organisms are homozygous for all the traits of interest
Single allele crosses ratios
Homozygous x Homozygous
1/1 AA or 1/1 Aa or 1/1 aa
Single allele crosses ratios
Homozygous x Heterozygous
1/2 AA OR 1/2 aa
AND 1/2 Aa
ex. 1/2 aa and 1/2 Aa
Single allele crosses ratios
Heterozygous x Heterozygous
1/4 AA, 1/2 Aa, 1/4 aa
How do you understand/figure out multiple allele crosses?
You multiply the single allele cross ratios
- MULTIPLY the denominators!
Pedigree Charts
What is the symbol for females?
Circles
Pedigree Charts
What is the symbol for males?
Squares
Pedigree Charts
What is the symbol for affected individuals?
A shaded circle/square is affected, not affected is not shaded
Where is genetic material at points exchanged during crossing over?
Chiasmas
What does autosomal dominant mean?
Non-sex gene, only 1 mutant gene required to cause disorder
equal frequency in both sexes!
What does autosomal recessive mean?
Non-sex gene, 2 mutant genes required to cause disorder
skipping of generations!
Linked genes
Different genes in close physical proximity on the same chromosome
Epistasis
Occurs when one gene affects the expression of a second gene
_____ changes can cause _____ twins to have different susceptibilities to the same disease.
Epigenetic, monozygotic
Recombination frequencies of _______ mean that the two genes are _______.
less than 50%, linked
Haplotype
Group of genes that are usually inherited together because they are located in close proximity to each other
What are the three types of sex-linked traits
X-linked dominant
X-linked recessive
Y-linked
X-linked dominant
sex gene, only 1 mutant gene required
dad affected, ALL daughters are affected
Dominant inheritance on the X chromosome. Any offspring (male or female) that receive the affected allele will end up with the disorder.
X-linked recessive
sex gene, 2 mutant genes required
Females: 2 affected alleles are needed to cause the disorder
Males: only 1 affected allele is needed to cause the disorder
more affected males!
Recessive inheritance on the X chromosome
Y-linked
sex gene
ALWAYS expressed, dominant or recessive because males only have one Y chromosome.
ONLY be passed from father to son (very rare)
How many X chromosomes do women have?
2 X chromosomes
Examples of X-linked recessive conditions.
Hemophilia and Color-blindness
Genomic imprinting
Genes that are expressed depending on parental origin
X-inactivation
Process by which one of a female’s X chromosomes is inactivated, forming a Barr body and preventing excess transcription
Female carrier can become affected
Epigenetics
Does not involve modifying the genetic code, but instead the regulation of when genes are expressed.
Examples of epigenetics
DNA methylation
Histone acetylation
Histone de-acetylation
Histone methylation
DNA methylation
Decreases gene expression by the suppression of genes. This is done through the addition of methyl groups, recruiting methyl-binding proteins (MBDs) and preventing transcription factors from binding.
Histone acetylation
causes gene activation and formation of euchromatin (easily accessible DNA).
Histone de-acetylation
causes gene suppression (think ‘de-activation’) and formation of heterochromatin (hard to access DNA).
Histone methylation
can upregulate/downregulate gene expression
Euchromatin
easily accessible DNA
Heterochromatin
hard to access DNA
Allele
one variation of a gene
