Unit 5 - Genetics

Phenylkentonuria (PKU)

autosomal recessive

sickle-cell anemia

autosomal recessive

tay-sachs disease

autosomal recessive

huntington’s disease

autosomal dominant

hemophelia

sex-linked recessive

red-green color blindness

sex-linked recessive

duchenne’s muscular dystrophy

sex-linked dominant

down syndrome

nondisjunction of chromosome 21

turner syndrome

nondisjunction of sex chromosomes (missing X chromosome)

klinefelter syndrome

nondisjunction of sex chromosomes (additional X chromosome)

cri du chat syndrome

deletion in chromosome 5

prader-willi syndrome

a disorder of chromosome 15 (an example of genomic imprinting)

angelmann syndrome

inheritance of the deletion from the mother on chromosome 15 (an example of genomic imprinting)

fragile X syndrome

most common inherited mental retardation disease; inherited from the father

cystic fibrosis

the most common inherited genetic disease in Europe and the US (autosomal recessive)

blending hypothesis

the old idea of genetics where scientists thought genetic material from parents mixed like blending paint in offspring —> we now know this is not true

Gregor (Johann) Mendel

“The Father of Modern Day Genetics”

Experimented with garden peas

character

gene —> a heritable feature

trait

allele —> the variant of a character

true breeding

purely homozygous —> same allele

continuum

more than 2 options —> a wide range of traits/alleles

Why did Mendel decide to only look at either-or traits?

This is important because be was able to focus on certain things to make his discoveries

What kind of pea plants did Mendel work with?

All the varieties that he worked with were “True Breeding”

P generation

parent generation

F1 generation

1st set of kids (filial generation)

F2 generation

2nd generation of kids (F1 generation = parents)

The results of Mendel’s experiments led to the formation of what 5 main ideas?

• There are alternate versions of genes called alleles

• Principle of Dominance

• For each character, an organism inherits 2 alleles

• Law of Segregation

• Law of Independent Assortment

phenotype

the result of the alleles that is physically expressed (physical tratis)

Principle of Dominance

• one gene may mask another

  • the dominant allele determines the organism’s appearance (it is expressed)

  • the recessive allele has no noticeable effect on the organism’s appearance (it is masked)

2 Alleles

for each character, an organism inherits 2 alleles (one from mom (egg) and one from dad (sperm))

Law of Segregation

the 2 alleles are separated into different gametes (during Meiosis) —> this means recessive traits show up in the F2 generation

Law of Independent Assortment

• members of one gene pair segregate independently of the members of the other gene pairs (homologous pairs separate independently during Anaphase I)

  • contributing factor to genetic diversity

genotype

the genes for the trait

testcross

used to determine if an organism is homozygous or heterozygous (never done on humans)

monohybrid cross

one characteristic/trait being crossed (traditional punnett square)

dihybrid cross

two character/traits being crossed

punnett square

the box we set up to do crosses

Reminders about Punnett square probability

a punnett square does not mean that two parents are going to have 4 kids and those are the kids they are going to have —> a punnett square simply shows what is the probability of those kinds of offspring

Rules of Probability: Rules of Multiplication

how to determine the chance that 2 independent events will occur together:

• flipping a coin

• chance of heads = ½

• chance of tails = ½

• chance of flipping heads THEN tails = ½ x ½ = ¼ = 25%

What are the odds of a couple having two biological female children then a biological male?

• chance of biological female = ½

• chance of biological male = ½

• chance of 2 biological females THEN one biological male

  • ½ x ½ x ½ = 12.5%

Rules of Addition

• the probability that an event can occur in two or more different ways

• used when the order is not specified and there is more than one way to get the outcome

• what is the probability that in flipping a coin we would get head AND tails (in no particular order)

  • Heads the first time = ½

  • tails the 2nd time = ½

    • ½ x ½ = ¼

  • tails the first time = ½

  • heads the 2nd time = ½

    • ½ x ½ = ¼

  • ¼ + ¼ = ½ = 50%

Codominance

both alleles are expressed

blood is an example (AB Blood —> both A and B are dominant and expressed)

multiple alleles

more than two alleles

ABO Blood

incomplete dominance

the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties (similar to the blending hypothesis situation)

pleiotropy

one gene has multiple phenotypic effects (meaning one gene has multiple effects in the body)

Examples are sickle cell disease and cystic fibrosis

epistasis

phenotype produced by alleles of one gene is influenced by a genotype of another

polygenic inheritance

more than one gene affects one phenotype

vary in the population along a continuum

opposite of pleitropy

A Blood

can only recieve A or O blood because it makes antigens against B

B Blood

can only recieve B or O blood because it makes antigens against A

AB Blood

can receive any blood type (universal receiver)

O Blood

can receive only O blood because makes antigens against both A and B (universal donor)

inherited disorders

• some are dominant

• some are recessive

• some are expressed based on age

pedigrees

a family tree that describes the interrelationships of parents and children across generations

genetic testing

for a growing number of diseases tests are available that identify carriers and help define the odds more accurately

fetal testing

• invasive (could possibly cause miscarriage)

  • amniocentesis/CVS

• non-invasive

  • ultrasound

amniocentesis

• the liquid that bathes the fetus is removed and tested

• the goal is to get a karyotype

• there are cells from the baby in the fluid - the cells are removed and a karyotype is produced

• typically done between 14-16 weeks of pregnancy

• invasive testing

chorionic villus sampling (CVS)

• a sample of the placenta is removed and tested

• goal is to get a karyotype

• done earlier in the pregnancy (8th-11th week)

• invasive testing

ultrasound

• non-invasive

• used for much more than pregnancies, but are a great way to check on the health of an unborn baby

• the ultrasound waves bounce off solid objects and create an image

• the 20th week ultrasound pregnancy is a very important test to see if there is anything wrong

alpha fetal protein (AFP)

• new test

• non-invasive “replacement” for amniocentesis/CVS

• blood test in combo with ultrasound

• blood test done to look for proteins in mom’s blood that would be released if the fetus has certain conditions

• early ultrasound dome to look at brain and heart development

Chromosome theory of Inheritance

chromosomes contain the info that gives us our characteristics (we don’t just randomly have genes floating around)

Sex Linked Traits

• Biological males (XY) only have one X, so they only have one “shot”. They only need one copy of the recessive allele to have that trait. This means we tend to see biological males exhibiting sex linked recessive traits

• Biological females (XX) can still have sex linked recessive traits, but it isn’t as common

linked genes

genes found on the SAME chromosome

genetic recombination

creates genetic variation

genetic recombination when genes are unlinked

• on two different chromosomes

• due to independent assortment

genetic recombination when genes are linked

• on same chromosomes

• due to crossing over

crossing over and linked genes

the closer two genes are to one another on a chromosome, the higher the chance those two genes will travel together during crossing over (which means less probability that crossing over will form new combinations)

linkage maps

mapping out chromosomes

linkage map rules

• if two genes are far apart, these is an increased probability that crossing over will separate them

• if 2 genes are close together, there is a smaller probability that crossing over will separate them

• we use recombination frequency - how often offspring show crossing over has occurred and translate that to a % called MAP UNITS (1% = 1 map unit)

sry

• a gene on the y chromosome

• the sex determining region of y

• it turns on when the embryo is about 2 months into development

x inactivation

• in biological females (XX) (must have at least 2 X chromosomes)

• only occurs in autosomes not gametes

• during embryonic development, one X in EACH cell is RANDOMLY inactivated

• the inactivated X condenses into what is called a BARR BODY

• the “blob” sits along the inside of the nuclear envelope

• this means that in each cell, there is either an active X from mom OR an active X from dad

• during cell division, they uncondensed and duplicate before condensing again

extranuclear genes

• genes not found in the nucleus (mitochondria and plastids) —> mitochondria have their own genes and DNA

• we can trace maternal lineage by looking at mitochondrial DNA because mitochondrial genes are only passed on by females NOT males

genomic imprinting

• some alleles have different results depending if it came from the egg or sperm

• the difference is the methylation of alleles (adding of methyl groups)

• examples include prader-willi and angelmann’s syndrome

nondisjunction

in meiosis, during anaphase I or II, chromosomes/chromatids do not separate properly leading to wrong numbers of chromosomes in gametes

deletion

a chunk of chromosome does not get copied and is deleted —> missing genes

duplication

chunk of chromosome copied extra times

inversion

when copied, order of genes in mixed up/reversed

translocation

not swapped with homologous pairs, instead swapped with another random chromosome pair

aneuploidy

not right number of chromosomes (only variation by a few chromosomes)

polyploidy

whole additional/missing sets of chromosomes