Bio ch 9 genetics Flashcards
what is the idea of pangenesis
particles called pangenes travel from each part of an organism’s body to the eggs or sperm and then are passed on to the next generation; changes that occur in the body during an organism’s life are also passed on in this way
what disproves pangenesis
- reproductive cells are not composed of particles from somatic (body) cells
- changes in somatic cells do not influence eggs or sperm
what is the blending hypothesis
the idea that the hereditary materials contributed by the male and female parents mix in forming the offspring and the original traits become lost
what disproves the blending hypothesis
it does not explain how traits that disappear in one generation can reappear in later ones
what is heredity
the transmission of traits from generation to the next
what is the field of genetics
the scientific study of heredity
who was Gregor Mendel
monk that bred garden peas
what did Mendel hypothesize
genes permanently retain their identities and do not blend
what is a character
a heritable feature that varies among individuals, such as flower color
what is a trait
each variant for a character, such as purple or white flowers
what is self-fertilization
the fertilization of plants by their own pollen rather than that of another individual
what is cross fertilization
fertilization of one plant by pollen from a different plant
how did mendel ensure self-fertilization when he wanted it
covering the flower with a small bag so no pollen from another plant could reach the carpel
how did mendel ensure cross fertilization when he wanted it
- prevented self-fertilization by cutting off the immature stamens of a plant before they produced pollen
- to cross-fertilize the stamenless flower, he dusted its carpel with pollen from another plant
- after pollination, the carpel developed into another pod containing seeds that 4. he planted
what are true-breeding varieties
varieties for which self-fertilization produced offspring all identical to the parent
what are hybrids
the offspring of 2 different varieties
what is the p generation
true breeding parental plants
what is the F1 generation
their hybrid offspring
what is the F2 generation
offspring when F1 plants self-fertilize or fertilize each other
what is a monohybrid cross
when the parent plants differ in only one character
what are Mendel’s laws
- there are alternative versions of genes that account for variations in inherited characteristics
- for each character, an organism inherits two alleles, one from each parent
- if the 2 alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant allele; the other has no noticeable effect on the organism’s appearance and is called the recessive allele
- a sperm or egg carries only one allele for each inherited character because allele pairs separate from each other during the production of gametes
what are alleles
alternative versions of a gene
what does homozygous mean
having 2 identical alleles for a gene
what does heterozygous mean
having 2 different alleles for a gene
what is a punnet square
shows possible combinations of alleles that could occur when gametes combine
what is phenotype
an organism’s physical traits
what is genotype
an organism’s genetic makeup
what is mendel’s law of segregation
pairs of alleles segregate during gamete formation
what is a dihybrid cross
a mating of parental varieties differing in 2 characters
what is dependent assortment
genes inherited as a set
what is independent assortment
genes inherited independently from each other
what is mendel’s law of independent assortment
the inheritance of one character has no effect on the inheritance of another
an event that is certain to occur has a probability of what
1
how can geneticists determine unknown genotypes
by performing a test cross with a homozygous recessive individual
an event that is certain to not occur has a probability of what
0
what is the rule of multiplication
The probability of two independent events is the product of the probabilities of each independent event. Ex. ½ x ½ = ¼
what is the rule of addition
the probability that an event can occur in 2 or more alternative ways is the sum of the separate probabilities of the different ways
what are wild-type traits
those prevailing in nature
what is a pedigree
a family tree based on a family’s history for the trait of interest
what are carriers
heterozygotes who have the recessive allele but are phenotypically normal
why are most genetic disorders not evenly distributed across all ethnic groups
possibly bc of prolonged geographic isolation of certain populations that led to inbreeding
why is inbreeding more likely to produce offspring homozygous for recessive traits
bc people with recent common ancestry are more likely to carry the same recessive alleles than unrelated people
why are dominant alleles that cause lethal diseases much less common than lethal recessives
bc the dominant allele cannot be carried without being expressed. Many lethal dominant alleles are fatal before the organism is even born, or before they are old enough to reproduce, thus the lethal allele is not passed on to future generations. In contrast, lethal recessive mutations are perpetuated from generation to generation by healthy carriers
what is achondroplasia
a dominant disorder that is a type of dwarfism in which the head and toros develop normally but the arms and legs are short
what is cystic fibrosis
a recessive genetic disorder characterized by an excessive secretion of very thick mucus from the lungs, pancreas, and other organs
what is huntington’s disease
a dominant degenerative disorder of the nervous system that does not usually appear until middle age
how can a lethal dominant allele escape elimination
if it does not cause death until a relatively advanced age
ex: huntington’s disease
what are examples of recessive disorders
Cystic fibrosis, PKU, sickle cell
what are examples of dominant disorders
Huntingtons disease
dwarfism
what is amniocentesis
a form of genetic testing before birth, performed between 14 and 20 weeks of pregnancy; a physician inserts a needle through the abdomen into the mother’s uterus to extract some amniotic fluid, which they then test for genetic disorders
what is chorionic villus sampling
a form of genetic testing before birth; a physician extracts a tiny sample of chorionic villus tissue from the placenta using a narrow, flexible tube inserted through the mothers vagina and cervix into the uterus. Results are available faster than amniocentesis and tests can be done earlier; however both cause risks so theyre reserved for situations where theres a higher possibility of genetic disease
what are some ethical considerations about genetic/fetal testing
- if confidentiality is breached, will carriers be stigmatized?
- who should pay for it?
- parents can choose between terminating the pregnancy or preparing themselves for a baby with severe problems
what is complete dominance
when the dominant allele has the same phenotypic effect whether present in one or two copies
what is incomplete dominance
Hybrids that have a phenotype in between the two parental varieties; the phenotypes of heterozygotes differ from the 2 homogenous varieties
why does incomplete dominance not support the blending hypothesis
bc the blending hypothesis predicts that the red and white traits could never be retrieved from the pink hybrids. however, these traits reappear in the f2 generation bc the red and white alleles segregate during gamete formation in the pink f1 hybrids
what antibodies are present in type a blood
anti-b
what types of blood does type a clot with
type b and type AB
what antibodies are present in type b blood
anti a
what types of blood does type b clot with
type a and type ab
what antibodies are present in type ab blood
none
what type of blood does type ab clot with
none
what type of antibodies are present in type O blood
anti a and anti b
what type of blood does type O clot with
a, ab, and b
which blood type is a universal donor
type O bc when donated it doesnt cause any clumping because it doesnt have any carbohydrates so nothing will be foreign to the recipient
which blood type is a universal recipient
type AB bc they can receive blood from anyone without risk of clumping because they have both carbohydrates so nothing introduced will be foreign to them
what are the 3 alleles responsible for blood type
IA, IB, and i; each person gets one of these alleles from each parent
what is codominance
when both alleles are expressed in heterozygous individuals (ex: IA AB (AB) blood)
when does blood clump with regard to blood transfusions
if the donor’s blood cels have a carbohydrate (a or b) that is foreign to the recipient
what is pleiotropy
when one gene influences multiple characters
what is an example of pleiotropy in humans
sickle-cell disease
what is the direct effect of the sickle cell allele
to make red blood cells produce abnormal hemoglobin proteins
how does sickle-cell disease exemplify the concept of pleiotropy
Homozygosity for the sickle-cell allele causes abnormal hemoglobin, and the impact of the abnormal hemoglobin on the shape of red blood cells leads to a cascade of symptoms in multiple organs of the body
what are the secondary effects of sickle-cell disease
kidney failure, heart failure, spleen damage, brain damage, pain and fever, joint problems, physical weakness, anemia, pnuemonia
why has sickle cell disease not gone extinct/why is is so common in african americans/africans
people with sickle cell are immune to malaria, so they live longer and have more offspring compared to noncarriers
what is polygenic inheritance
when many genes contribute to a single characteristic
what is an example of polygenic inheritance
skin color, eye color, hair color
why will a purely genetic description of skin color always be incomplete
bc some intermediate shades of skin color result from the effects of environmental factors, such as exposure to the sun
what are examples of how the environment affects phenotype
- the leaves of a tree might all have the same genotype, but they may vary greatly in size, shape, and color depending on exposure to wind and sun and the tree’s nutritional state
- in humans, nutrition alters height, exercise alters build
are many human phenotypes influenced by both genes and environment?
yes
what is one character that is not influenced at all by the environment
blood type
what is the important difference between traits affected by a persons genes and the environment
only genetic influences are inherited; any effects of the environment are generally not passed down to the next generation
what is the chromosome theory of inheritance
genes have loci on the chromosomes and it is the chromosomes that segregate during meiosis
what is the chromosomal basis for the law of independent assortment
the non homologous chromosomes (and their genes) assort independently in metaphase 1 leading to 4 gamete genotypes
what are linked genes
genes located close together on the same chromosome that tend to be inherited together; generally do not follow mendel’s law of independent assortment; meiosis will yield mostly two genotypes of gametes rather than equal numbers of the four types of gametes that would result otherwise
what is the recombination frequency
the percent of recombinants; # recombinant/# offspringw
what are recombinant gametes
ones that are created from crossing over - not the parental phenotype
what is genetic mapping
where on the chromosome are specific genes located
what is a linkage map
a diagram of relative gene locations
what is the real beauty of the linkage mapping method
a wealth of information about genes can be learned simply by breeding and observing the organisms - no fancy equipment
what is important about the SRY gene on the y chromosome
triggers testis development
what is a sex-linked gene
a gene located on either sex chromosome
