Unit 5 - Heredity Flashcards
what is made by meiosis
gametes
gametes
- sex cells
- sperm or egg
- haploid
egg cells are also known as
oocyte
what are haploids
- 1 set of chromosomes
- “n”
- humans = 23
gametogenisis
- making gametes
fertilization
- sperm and egg unite and the diploid number is restored
diploid
- 2n
- a pair of each chromosome
- # in a body cell
- humans = 46
kareotypes
- picture of the chromosomes in order
homologous chromosomes
- SEPERATE chromosomes
- code for the same traits
- you get one from mom and one from dad
sister chromatids
- two legs of A CHROMOSOME
what does mitosis make
- makes 2 genetically identical daughter cells
what does meiosis make
- make the gametes
- genetically different
- “reduction division”
interphase (meiosis)
- duplicate the DNA
- start with 6 chromosomes
meiosis 1: prophase 1
- homologous chromosomes pair up (aka: synapsis)
- tetrad
-crossing over: genes will mix between chromosomes
tetrad
homologous pair
chiasma
- where the crossing over takes place
what provides variety in meiosis
- crossing over
- random assortment of chromosomes
meiosis 1: metaphase 1
- homologous chromosomes line up
- law of independent assortment
meiosis 1: anaphase 1
- homologous pairs will separate
** nondisjunction -> trisomy 21
meiosis 1: telophase 1 + cytokinesis
- 2 genetically different haploid cells
why is interphase missing between meiosis 1 and 2?
- you don’t want to replicate (no s-phase)
meiosis 2: prophase 2
- nuclear envelope breaks down
meiosis 2: metaphase 2
- sister chromatids line up
meiosis 2: anaphase 2
- sister chromatids are pulled apart
law of segregation
**
- variety
law of independent assortment
meiosis 2: telophase 2 and cytokinesis
- 4 genetically different haploid cells
- 4x sperm cells
- 1x egg cell
- 3x polar bodies
diploid cells have
pairs of chromosomes (a full set)
- one from each parent
how does crossing over increase genetic diversity
- it occurs in prophase 1 of meiosis 1
- nonsister chromatids of double homologous chromosomes exchange segments
- results in recombinant chromatids
homologous chromosomes
carry information for the same genes, one from each parent
what does crossing over result in
recombinant chromatidsn -> increases genetic diversity
autosomal inheritance
- inherit 2 of every kind
- this refers to the transmission of genetic traits that are determined by genes located on the autosomes (non-sex chromosomes)
how many pairs of autosomes do humans have
22 pairs
which genes are inherited as autosomal traits?
AA, Ee, bb
which genes are inherited as sex linked traits
- sex linked traits are only inherited on x-chromosome
phenotype
- physical traits
- traits that you see
genotype
- genes that code for the phenotype
allele
different forms of a gene
ex: blue/brown eyes
how does the genotype determine the phenotype
- the genotype codes for the protein OR lack of
- then: phenotype is either the expression/no expression of protein
homozygous dominant
BB
homozygous recessive
bb
heterozygous
Bb
what is meant by autosomal
- chromosomes that are 1-22
locus
physical location of the gene
what is dominant true breeding also known as
homozygous dominant
what is recessive true breeding also known as
homozygous recessive
other names for heterozygous
hybrid OR carrier
P generation
parental generation
F1 generation
- the first generation of offspring resulting from a cross between two parent organisms
F2 generation
- the result of a cross between individuals from the F1 generation
wild-type
- the original version of a gene
- “found in nature”
blood clotting
- mutant version, clots last longer
what alleles could parents Bb x Bb pass on to their offspring
BB, Bb, Bb, bb
if a person has the dominant phenotype do we know their genotype by just looking at them?
- no, a person could be homozygous dominant or heterozygous
what if a person has the recessive phenotype, do we know their genotype just by looking at them?
yes, in order to be recessive, you must be homozygous
laws of probability (addition)
- the addition rule is used to find the probability of an event happening when the outcomes CANNOT happen simultaneously
dihybrid crosses
laws of probability (multiplication)
-
incomplete dominance
neither allele is dominant over the other
p-gen: BB x bb
codominance
p-gen: BB x bb
both alleles are expressed in the heterozygous conditions
multiple alleles and codominance: blood types
A
B
AB
O
blood type A
AA or Ai or iAiA or iAi
blood type B
BB or Bi or iBiB or iBi
blood type AB
AB or iAiB
blood type O
oo or ii
polygenic inheritance
- multiple genes controlling a phenotype (traits)
ex: skin color
epistasis
- multiple genes controlling a specific phenotype/trait
- there is also a gene that modifies or represses the trait
linked traits
genes that are on/inherited on the same chromosome
if genes are located on different chromosomes they assort…
independently and you can expect a 1:1:1:1
if the genes are all recessive, does it matter that they are linked
- no
parental offspring
- they look like the parents because they are linked
- only 2 possible types of phenotypes in the offspring
monohybrid crosses: AA x aa
Aa - 100%
monohybrid crosses: Aa x aa
Aa - 50%
aa - 50%
monohybrid crosses: Aa x Aa
1:2:1
AA, Aa, aa
test cross means to cross with
full recessive
RrTt x RrTt - ratio
9:3:3:1
RrTt x rrtt - ratio
1:1:1:1
in the fly experiment, why were the proportions of fly phenotypes so off?
the genes for the body color and wing shape are linked (on same chromosome)
what process led to the two recombinant offspring?
crossing over (chiasma)
what can we do with the number of recombinant offspring info?
we can see how close the genes are on the chromosome
- closer they are = less recombination (think of shuffling cards in a deck)
recombinant frequency
equation: (# of recombinant offspring / total offspring) x 100
- can be used in gene mapping
- expressed in map units
review: autosomal
- genes inherited from body cells -> one from mom and one from dad
- 22 pairs (44 total)
sex linked inheritance
- X - from mom
- X or Y - from dad
females sex chromosome
XX
males sex chromosome
XY
which sex chromosome carries the gene
X
explain a male carrying two X- chromosomes
if a male carries 2 x-chromosomes, the healthy/disease free X will be the dominant phenotype
color blindness
- sex linked recessive trait
patterns of inheritance
- dominant
- recessive
- autosomal
- sex linked
- mitochondrial
allele
one of several varieties of a gene
- no organism can have more than two alleles for any given trait
ex: purple or white
mendel’s law of independent assortment
- genes on different chromosomes segregate their alleles independently of each other
in a monohybrid cross, note that if P is pure dominant, the F2 phenotypes will be in a 3:1 dominant:recessive ratio
monohybrid cross
- cross involving a single trait
dihybrid cross
- cross involving two traits
complete dominance
a dominant allele is expressed over a recessive allele
incomplete dominance
an intermediate phenotypes of the two alleles
codominance
- both alleles are expressed
ex: blood types
chromosomal theory inheritance
- explains heredity in terms of chromosomes
- explains appearance of new traits in terms of genetic recombination due to synapsis and law of ind. assortment
- explains diseases due to mutations on chromosomes or due to incorrrect # of chromosomes
- explains why some traits almost always get inherited together (linked genes)
aneuploidy
- an incorrect number (too many or too few) of chromosomes
- results from nondisjunction
nondisjunction
the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally
down syndrome
- nondisjunction of chromosome 21 during meiosis 1
- aka trisomy 21
nonnuclear inheritance aka
- maternal inheritance
- mitochondrial inheritance
is crossing over more likely to occur if genes are closer together or further apart on a chromosome
further apart
why are linked genes inherited together?
because they are so close on the same chromosome that very little crossing over occurs
how to decide whether genes are linked or not linked
- compare the phenotypes of the offspring to the phenotypes of the parents
- if most offspring resemble the parents for both traits, with very few recombinant offspring = linked
non-nuclear DNA
- traits determined by chloroplasts and mitochondrial DNA that do not follow Mendelian rules
pedigree charts: mitochondrial inheritance
mom passes the trait to all children
hydrangeas
the pH of the soil will affect the color (phenotype) of the hydrangeas
arctic fox & hare
- the amount of light affects the phenotype of fur coat
ex: less light -> less melanin
phenotypic plasticity
- occurs when individuals with the same genotype exhibit different phenotypes in different environments
what may lead to phenotypic plasticity
- environmental factors influence gene expression and can lead to phenotypic plasticity
explain reptiles and sex determination
- temperature determines sex
- this happens because temperature changes which genes are expressed
UV light effect on gene expression
- as UV light increases, melanin production increases
certain human genetic disorders can be attributed to
the inheritance of a single affect or mutated allele or specific chromosomal changes, such as nondisjunction
sickle cell anemia
point mutation
tay sachs
- lethal
- most live up to age 3-5 yo
- autosomal recessive disorder
- accumulation of fat in the nervous system due to a lysosome malfunction; does not make a protein that breaks down the fat
huntingtons disease
- adult onset (35 years)
- leads to loss of cognative ability, dimentia
- autosomal dominant trait
- lethal
- due to a repeat CAG
what is considered a “normal” number of repeats of CAG
- 26x or less
what is considered a “abnormal” (huntingtons) number of repeats of CAG
- 40x or more
nondisjunction
unequal splitting of chromosomes in anaphase
aneuploid
something wrong with chromosome number
trisomy
- n + 1
- extra chromosome
how does the sperm cell determine your sex?
there are 22 regular chromosomes in the sperms nucleus, the 23rd is your sex-determining chromosome
if this is x = girl
y = boy
zygote
a fertilized egg
- 46 chromosomes OR 23 pairs of homologous chromosomes`
in pedigree charts, whats one giveaway for sex-linked
dad has the trait and passes it onto the daughter
gene
a section of DNA that codes for a certain protein, which can be responsible for the expression of certain traits
trait
an observable characteristic of an organism
allele
one of the determining factors in the expression of a gene
- traits are typically expressed depending on the certain combination of these
phenotype
the set/collection of observable characteristics of an organism, determined by the ways in which the genotype is expressed
law of segregation
- during the production of gametes, the alleles that code for the same gene are split (segregated), and the gametes carry half of genetic material.
- we now know that this is due to anaphase I in meiosis.
true breeding
crossing organisms that are homozygous, either recessive or dominant
phenotypic ratios for dihybrid crosses
9:3:3:1
probability of a specific trait set
- if asked for a specific trait/genotype, calculate the independent probabilities of each trait combo then multiply
what is mendel’s form of dominance referred to as
complete dominance
the chromosomal theory of inheritance explains
- recombination is determined by synapsis and independent assortment
- explains sex linked traits
- diseases caused by mutation or incorrect chromosome count
sex linked traits
traits determined by the x-chromosome
sex limited traits
traits only exhibited by one sex or the other
differences in sex-linked trait expression
- females have 2 X’s therefore if one is dominant, that is what will be expressed
- males only have 1 X, so any trait expressed in the area will be the result
X^N X^N
normal female
X^n
affected male
males inherit their X-linked traits from where
their mothers
what distance of genes has a higher chance at crossing over
genes far apart on chromosomes have a higher chance of crossing over and becoming recombinant
phenotypic plasticity
the property of an organism’s phenotype to change due to factors presented in the environment, influencing the expression of certain genes
chi square usage
used to determine if there is a statistically significant difference between the expected results and the observed results in an experiment or study
