mod 6: Mendelian Genetics Flashcards
selective breeding
choosing stock because of its physical, behavioural, or functional characteristics
inheritable trait
a characteristic determined by genes, not environment. a trait that is capable of being passed from parent to offspring
true breeding
an organism that is true breeding produces offspring that express the same trait generation after generation. the organism is homozygous for a trait
hybrid
offspring of a cross between two parent organisms with different inheritable traits
mono hybrid cross
an organism that is heterozygous for one trait
P1 generation
P generation
the first set of parents. the parents of the F1 generation
Fx generation
F1, F2, etc.
F1 are offspring of the P generation. F(1+x) are offspring of the Fx generation (F5 offspring of F4).
filial generation—brothers and sisters
pangenesis
Aristotle’s theory that that sperm and eggs consist of particles called pangenes from all the parts of the body. when fertilization occurs, pangenes develop into the body part they were derived from
homunculus
a complete miniature person within a sperm cell (proposed and first identified by Leeuwenhoek) or an egg cell (suggested by Graaf). it was first “identified” by Leeuwenhoek when he looked through his 500x microscope at the head of a sperm. Graaf suggested that the homunculus is within the egg cell and that the sperm only stimulates it to develop
homozygous
a genotype where both alleles are the same (ex: RR or rr)
heterozygous
a genotype where the alleles are different (ex: Rr)
genotype
the alleles an organism has for a specific trait (ex: RR, Rr, or rr)
phenotype
the observable characteristic of the organism (ex: tall or short). determined by genotype
dominant
if two alleles are present then the ones that is expressed is the dominant one. written as a capital letter. expressed when homozygous (RR) or heterozygous (Rr)
recessive
if two different alleles are present, the allele that is not expressed (is masked by the dominant allele) is recessive. written as a lowercase letter. only expressed when homozygous (rr)
allele
two or more forms of a gene in a specific location on the chromosome
gene
an area on the chromosome that defines an organism’s traits
law of segregation
Mendel’s first law
• discrete genes determine individual traits
• each individual organism has two copies of each gene
• when gametes are formed, the copies of the factors segregate so that the gamete receives one copy of each factor
• eggs and sperm fuse randomly. the embryo that develops has two copies of each factor—one copy from each parent
addition rule (probability)
if two outcomes are mutually exclusive (you can have one but not the other), the probability that either will occur is their sum.
(ex: the probability that you will roll a 3 or a 4 on six sides die is 1/6 + 1/6 = 2/6 = 0.33 = 33%)
multiplication rule (probability)
if two outcomes are independent, the probability that both will occur is their product.
(ex: the probability that you will role two 4s on two six sided die at once is 1/6 x 1/6 = 1/36 = 0.03 = 3%)
nature (in reference to nature vs. nurture debate)
refers to the components of an individual’s phenotype that is determined by their genes
nurture (in reference to nature vs. nurture debate)
refers to component of one’s phenotypes determined by their environment
innate
an innate characteristic is one a person is born with
dihybrid
a genotype that is heterozygous for two traits (AaBb). sometimes used to refer to genetics problems using two traits
trihybrid
genotype that is heterozygous for three traits (AaBbCc). sometimes used as a general way to refer to genetics problems using three traits
law of independent assortment
Mendel’s second law. the two alleles of one gene segregate independently of the other alleles of other genes during gamete formation
what is the F2 ratio of phenotypes in Mendel’s dihybrid crosses?
9:3:3:1
test cross
determines the genotype of an individual with a dominant phenotype by crossing them with a homozygous recessive individual—if any offspring have the recessive phenotype then the unknown is heterozygous
what information is provided in a Punnett square?
all possible gamete formations from the P generation, all possible genotypes of the F1 generation, and the ratios of the possible genotypes of the F1 generation
progeny
descendants of an organism. offspring
sickle cell anemia (SCA)
autosomal recessive disease that causes sickle-shaped red blood cells to form, which can get caught in blood vessels and stop flow to tissues. note: exhibits incomplete dominance—heterozygotes rarely have any symptoms are are unlikely to develop sickle-shaped blood but are still resistant to malaria, an example of heterozygote advantage
autosomal
refers to a trait that is due to a gene on one of the first 22 chromosomes (any chromosomes, excluding the sex chromosomes). since this excludes sex chromosomes it is equally likely in male and females
multiple alleles
some genes have more than two alleles. an order of dominance is given to determine phenotypes from genotypes.
incomplete dominance
condition where neither of two alleles of the same gene can completely conceal the presence of the other, causing the heterozygous to be a mixture of the two rather than one or the other
heterozygote advantage
when heterozygous individuals have an advantage over homozygous recessive or homozygous dominant individuals
co-dominance
situation where both alleles are fully expressed (ex: a roan horse is a heterozygote in which the base colour and white are both fully expressed, giving it a paler look from farther away, caused by individual hairs being completely white and others being completely base colour)
continuous trait
traits for which the phenotypes vary gradually from one extreme to another. polygenic
(ex: height in humans)
polygenic trait
controlled by many genes. group of genes contributing to a trait is called a polygene. each dominant allele contributes to the trait, recessive alleles do not contribute (ex: more dominant alleles equals greater height)
pedigree
chart outlining the generations and relationships within a family line. used to study inheritance of genetic diseases or conditions in humans
chromosome theory of inheritance
Walter Sutton’s theory that chromosomes are strings of genes and that each gene has a specific location on a specific chromosome
Barr bodies
in every female cell one of the X chromosomes is inactive, and condensed tightly into a Barr body. either X chromosome can be inactive and which one becomes inactive and forms a Barr body is random.
(ex: this can cause effects like calico cats, where the colour of fur is heterozygous and linked to the X chromosome, so the colour of the patches on the cat is determined by which X chromosomes ends up deactivated)
sex-linked traits
traits found in one gender more than another due to the gene being present on sex chromosomes
hemizygous
used when referring to the X chromosome of someone with XY sex chromosomes because, since they have only one X chromosome, the terms heterozygous and homozygous don’t work
hemophilia
X-linked recessive. characterized by inability to clot blood. caused be recessive allele of Factor VIII gene on X chromosome
polygenic inheritance
where more than one gene are involved in determining the phenotype for one characteristic. the ratio of phenotypes tends to stay at 9:3:3:1, the only difference is that instead of different combinations of two traits, there are four varieties of one trait
epistasis
type of polygenic inheritance where one set of genes will interfere with or affect the expression of another set of genes. unusual ratios (ratios that aren’t 9:3:3:1) are characteristic of epistasis
(ex: fur colour in mice depends on a gene for colour and a separate gene for pigmentation of colour, so the gene for pigmentation can interfere with the gene for colour and produce a white mouse when the colour according to the gene should be black, for example)
pleiotropy
when one gene influences many different traits
exception to independent assortment?
when the genes are linked genes they tend to stay together. they can be separated during the process of crossing over, and the greater the distance between them the greater the number of crossover events that will occur between them, and therefore the greater the chance that they will be separated, but separation of linked genes isn’t entirely random like it is with genes on different chromosomes.
linked genes
genes that exist on the same chromosome
chromosomal mapping
the process of using the concept of crossing over to determine relative positions of genes on a chromosome
map unit
the distance between points on a chromosome where crossover is likely to occur in 1% of all meiotic events.
directly proportional to recombination frequency (1 map unit = 1% recombination frequency)
used to create a chromosome map showing the relative distances between linked genes
map distance
distance between genes on a single chromosome
recombinant types / recombinants
the offspring that don’t look like parents in a linked gene cross. result of crossing over in chromosomes
parental type
offspring of a linked gene cross that have identical chromosomes to their parents
recombination frequency
the percentage of offspring that were recombinant types—the percentage of times that a crossover occurred as P generation gametes were being formed.
directly proportional to map unit (1% = 1 map unit)
recombination frequency = [(recombinants)/(total offspring)]•100
