BIOL20 - Heredity

Genetic info

carried on chromosomes

• equal # in sperm + egg

Homologous pairs

• 23 chromosomes

• one set from each parent

• each parent carries genes for the same traits

Genes

segments of DNA

• code for specific protein

• units of info abt a specific trait

Trait

characterisitc

Alleles

diff forms of a gene that produce diff versions of the trait

ex: gene for freckles

Homozygous

2 copies of the same allele

Heterozygous

diff alleles of a given gene

Dominant

effects of the allele are detected regardless of the alternative allele

Recessive

effects of the allele are masked in the heterozygous condition

Genotype

alleles are present for a gene

• molecular genetic components

Phenotype

observable traits of an individual

• observable trait

Law of segregation

2 alleles for each gene separate

Law of independent assortment

each chromosome = inherited independently of the other chromosomes

Mendelian genetics

how single genes are inherited from parent - offspring

Punnett square

row → possible gametes of 1 parent

columns → possible gametes of other parent

boxes → possible combos of gametes

predicts genetic makeup of offspring

Monohybrid cross

both parents = heterozygous for one trait of interest

Ratio = 1 FF: 2 Ff: 1 ff

Dihybrid cross

both parents = heterozygous for 2 traits of interest

ratio = 9:3:3:1

Polygenic inheritance

most inherited traits are NOT controlled by one gene

Complex inheritance

combined effects of many genes + environmental factors

• skin color, hair color, height, metabolism rate, body build

Ex of complex trait

skin = depends on environmental conditions (sun exposure, nutrition, and genes)

Autosomes

22 pairs of chromosomes with the same appearance in males and females

Sex chromosomes

XX = female

XY =male

23 chromosome

Sex linked genes

genes on the same sex chromosome (X or Y)

Y-linked

rare

Y is much smaller than X → carries less genes

X-linked genes

more common

most genes on X chromosome

• males only have one X

E.g. X-linked d/os

red-green color blindness

hemophilia

duchenne muscular dystrophy

• all more common in men bc they only need one X chromosome to have the gene to present it

Sex determination

males produce sperm carrying an X or Y

• sex determined by father

• Y initiates male pattern of development

Sex-linked inheritance

females can either be normal, carriers, or have the trait

• men can only be normal or have the trait

Genetic d/os

often caused by recessive alleles

Carriers

displays the dominant type, but is heterozygous for the trait (carries recessive allele)

Nondisjunction

error in cell division → abnormal # of chromosomes

Aneuploid

chromosomes added or missing

• monosomic cell missing 1 chromosome

• trisomic cell has an additional chromosome

  • ex: down syndrome → three 21st chromosomes

Albinism

dominant allele produces a f(x)nal protein but recessive doesn’t

• lacks ability to produce melanin

• dominant → pigmentation produces tyrosinase

• recessive → produces nonf(x)nal tyrosinase

tyrosinase=ability to produce melanin

Pleiotropy

one gene has many effects

ex: sickle cell anemia

• sickling of RBCs caused by abnormal hemoglobin → affects body

  • clog blood vessels

  • accumulate in spleen

Breaks in chromosomes caused by

• chemicals, radiation, viruses

results in:

• changes in structure + f(x) of chromosome

• deletion + duplication

Deletion of chromosomes

loss a piece of chromosome

• most common = tip breaks off

• ex: cri-du-chat syndrome → loss of #5 tip

Duplication of chromosomes

addition of piece of chromosome

• effects depend on size + position of the addition

• ex: fragile x syndrome → duplication of a region of X chromosome

Invasive detection of genetic d/os

• amniocentesis = sample of amniotic fluid

• chorionic villi sampling (CVS)

Non-invasive prenatal screening

• sampling of fetal cell - free DNA

• found in maternal blood

disadvantages:

• higher rate of false positives

advantages:

• don’t risk miscarriage

• can be done earlier in pregnancy

Newborn genetic testing

blood test screens phenylketouria (PKU)

• means baby can’t process phenylalanine

Adult genetic testing

predictive generic tests available + being developed

at risk/predisposed for a specific disease before symptoms appear