Chapter 10 Flashcards
trait
a variation of a particular chracter
pattern of inheritance
the way characteristics are transferred from parents to offspring
blending hypothesis of inheritance
stated that genetic material from parents mixed to create a new trait which would then be inherited by the offpspring
disproving the blending hypothesis
the blending hypothesis failed to explain how traits disappear in 1 generation and reappear in later ones
genetics
the study of heredity
particulate hypothesis of inheritance
parents pass on to their offsprng sepearet and distinct factors (now referred to as genes) that are responsible for inherited traits. these heritable factors retain their identity generation after generation
self-fertilisation
sperm from the pollen of a flower fertilising the eggs in the flower of the same plant. when both male and female gametes are produced by the same individuals and result in fertilisation
cross-fertilisation
sperm from the pollen of one flower fertilising the eggs in the flower of a different plant
true-breeding
when a plant produces off spring identical in appearance to itself generation after generation when self-fertilised. caused by having homozygous alleles
how did mendel test the particulate hypothesis and ensure cross fertilisation
to test the particulate hypothesis, mendel crossed true breeding plants that had 2 distinct and contrasting traits-for example, purple or white flowers who would serve as parents for the next generation. he crossed the two by first, cutting of the immature stamens off of one flower to prevent self fertilisation and then dusting the carpel with pollen from another plants nature stamens to cause fertilisation.
how did mendel ensure self-fertilisation
to ensure self fertilisation mendel tied a cloth bag around the bushes with the true breeding pea plants’ flowers so that pollen from other plants could not enter
how does the particulate hypothesis differ form the beldning hypothesis
the blending hypothesis stated that genetic material from parents mixed to create a new trait which would then be inherited by the offspring, however, the particlate hypothesis stated that parents pass on to their offsprng sepearet and distinct factors (now referred to as genes) that are responsible for inherited traits. these heritable factors retain their identity generation after generation, and thus, unlike in the blending hypothesis, do not mix
the difference between self fertilisatiion and cross fertilisati
self fertilisation occurs when sperm from the pollen of a flower fertilising the eggs in the flower of the same plant. when both male and female gametes are produced by the same individuals and result in fertilisation, cross fertilisation however occurs when sperm from the pollen of a flower fertilises the eggs in the flower of a different plant
hybrid
the offspring of 2 different true breeding varieties
monohybrid cross
a pairing in which the parent plants differ in only one character
2 alleles for
every genes in an organisms cells
punnett square
diagram that shows all possible outcomes of a genetic cross. used to predict probabilities of particular outcomes if the genotypes of both parents are known
mendels four hypothesis
1- there are alternate forms of gnees called alleles
2- for each inherited character an organism has 2 alleles for the gene controlling that character , one form each parent. if the two allels are the same, the individual is homozygous for that character. if the two alles are different the individual is heterozygous
3-when only 1 of the two different alles in a heterozygous individual appears to affect that trait, the allele is called the dominant allele. and in such cases the other allel that does not appear to affect the trait is called the recssive allele
4_ the principle of segregagtion: two allels for a character segregate during the formation of gametes so that each gamate carries only 1 allels for each character
genptype
the genetic makeup or combinnation of alleles
phenttype
the observable or physiological traits of an individual
testcross
breeidng an indivual of unknown genotype but dominant phentoype with a homozygous recessive individual. the appearance of the offspring resulting from the testcross will reveal the genotype of the mystery parent because the homozygous recessive parent can only contribute a recessive allele to the offspring,, the phenotype will indicate the llele contributed by the mystery plant. if the mysteryparent is homozygous dominant, all offspring would have the dominant phenotype, but if it is heterozygous the the phenotypic ratio of dominant to recessive would be 1/2:1/2
dihybrid crosss
crossing organisms that differ in two chracters
principle of independant assortment
during gamate formation in an f2cross, a particular allele for one character can be paured with either allele of another character and are sorted into gamates independently of one another
dihybrid F1 cross ration
9:3:3:1
intermediate f2 cross ratio
1:2:1
intermediate inheritance
for some characters of organisms neitehr allee is dominant the heterozygotes have a phenotype that is intermediate between the phenotypes of the two homozygotes.
multiple alleles
for some genes severeal alles exist in the population which expand the variety and number of possible genotypes and phenotypes
when more than 2 alles affect a gene
codominance
a type of inheritance iin which 2 alles of the same gene are expressed saparatel to yield different traits in an individual
characteristic of mendelian genetics
-principle of segregaion
-principle of independant assortment
-law of dominance and uniformity
difference between intermedite inheritance and codominance
unlike in intermediate inheritance, the phenotype is no intermediate but rather shows the separate traits of both alleles
law of dominance and uniformity
some alles are variants of a particular gene found at the same chromosmsomal locus are dominant over other alles of a given gene unless both alles are recessive
polygenic inhertiance and its effects on the population
when 2 or more genes affect a single character
the potential combinations of alleles an dthus range in phenotype increases with the number of genes that affect that character
what environmental factors affect which human traits
nutrition- height
exercise-build
exposue to sunlight- skin tone
altitude of ones home, physical activity level, presence of infection- blood count
phenotypic ratio for dominant recessie f2 cross
3:1
what is the likely echanism of inheritance for a character with a large range of phenoypes
polygenic inheritance. polygenic inheritance is when 2 or more genes affect a single character. the potential combinations of alleses (and subsequently the range of phenotypes) for a certain character increases proportionally with an increase in the number of genes that effect it, thus augmenting the range of phenotypes got that character
chromosome theory of inheritance
genes are located on chromosomes and the behaviour of chromosomes during meirosis an feritilisation accounts for inheritance patterns. indeed it is chromosomes that unergo segregation and independent assortment during meiosis and thus account for mendels two principes
locus
the location of a gene on a chromsomes
location of allels
alles of a gene reside at the same gene locus on homologous chromsomes
genetic linkage
the tendency for alles on one chromsome to be inherited together
what affects genetic linkage
the closer 2 genes are on the same chromosme the greater the genetic linkage. the farther apart the genes are the more likely it is that a crossover events will separate them
exceptions to independant assortment and segregation
when genes are loacted on separate chromsomes they sor indepensdantl of each other during meiosis and are sorted into different gamates but when genes are located on the same chromosome and exhibit great genetic linkage (that is, their loci are close together) their allles would not tend to be sorted into gamates independently as they would stay together during meiosis.
sex linked gene
any gene that is located ona sex chromosome
most sex linked genes are x-linked as the X chromosome is much larger and contains more genes than the Y chromsome
why are sex-linked disorders more prevalent amngst men
sex-linked siroders are more rpevalent amongst the male population s most sex linked disorders are x linked and recessive, meaning that if a male (who would have only 1 x chromosome) were to inherit a single copy of the disorder’s allles, it would be expressed as only 1 copy of the recessive alle would be necessary. females on the other hand would need 2 copies of the recessive alle in order to express the disorder which is much less likely to happen in comparison to men as the probability of a single parent having the disorder is greater than both having it and subsseuqnetly passing it on.
