Mendel and the Gene Idea Flashcards
who is gregor mendel and what did he do?
gregor mendel discovered the basic principles of heredity through his work with garden peas.
by the 1800s, what was the favoured explanation of heredity?
the blending hypothesis: if you have a dark skin person and a light skin person having a kid, the baby will be medium skin tone.
did mendel agree or disagree with the blending hypothesis?
mendel disagreed with the blending hypothesis.
- he showed that discrete heritable units such as genes are passed on from parents to offspring. these genes maintain their distinct identities in offspring from generation to generation.
what did mendel study?
mendel studied 7 different characters of pea plants.
what is a character?
a character is visible feature of an organism. example: flower color, plant size
what is a trait?
a trait is variations of a character. example: purple flower, white flower, tall plant, short plant
what was the advantage of using the pea plant for his experiment?
- easy to grow
- grow to maturity in a single season
- many varieties
- easy to cross breed experimentally
what did mendel do in his experiment?
in his experiments, mendel crossed two contrasting, true breeding, varieties of pea plants. this meant he used one plant that always produces purple flowers: PP. and another plant that always produces white flowers: pp. he crossed these CONTRASTING TRUE BREEDING varieties of pea plants.
what does true breeding mean?
upon self pollination, an organism will produce offspring with the same traits. example: a true breeding purple flowered plant always produces offspring with purple flowers because the genetic makeup is PP: HOMOZYGOUS.
carpel vs stamen?
the carpel is the female reproductive organ: stigma, style, ovary
the stamen is the male reproductive organ: anther, filament
what does the fertilized ovule turn into? what does the mature ovary turn into?
the fertilized ovule turns into a seed.
the mature ovary turns into a fruit.
so what did mendel cross?
mendel crossed two true breeding parents.
purple flowered pea plant (female) x white flowered pea plant (male).
he CROSS POLLINATED THEM.
what is cross pollination?
cross pollination is when the pollen from the anthers of one flower is transferred to the stigma of another flower.
why is cross pollination important?
cross important is important because it increases genetic diversity which can improve resilience to diseases and environmental changes.
how exactly was cross pollination carried out?
- to prevent self pollination, the anthers of the receiving plant are cut.
- pollen is collected from the anthers of the white pea plant.
- the pollen is transferred to the stigma of the purple pea plant.
- fertilization occurs and ovules turn into seeds. the seeds contain a mix of genetic material from both the white and purple pea plants.
- the fertilized seeds are planted and when they grow into new plants, they are called the offspring: F1 generation. this is the step where the offsprings traits like flower color are observed.
what was the result of this (what color were the plants)
all offspring of F1 generation were purple. this is because the purple allele P is dominant over the white allele p.
is the white trait gone?
the white trait is not gone. it is still present in the F1 generations genetic makeup, it is just recessive and hidden by the dominant purple allele.
if the pollen from the purple flower was used instead, what would happen?
the same result: the flowers would be purple.
what is a reciprocal cross?
crosses made in both ways that end up with the same results are called reciprocal crosses
cross 1: use pollen from white flower and fertilize the purple flower.
cross 2: use pollen from the purple flower and fertilize the white flower.
in both cases f1 generation would still have the same result.
since the same result is observed, what can we conclude?
we can conclude that the character is NOT SEX DEPENDENT. the outcome is the same regardless of male or female. this means: gene for that character is not located on a sex chromosome.
what does selfing mean?
self fertilization
what did mendel do after the f1?
after obtaining the f1 generation from the initial crosses, he allowed the f1 plants to self pollinate which created the f2 generation.
what was observed in f2?
a 3:1 ratio was observed in f2.
3 purple flowered plants 75%
1 white flowered plant 25%
why is one flower white here?
the white flower appears in the f2 generation because when the f1 generation self pollinated, it resulted in one flower having two recessive alleles. pp.
what is an allele?
alternative versions of a gene. each organism has two alleles for each gene: one from each parent.
parent 1: purple flower: two identical alleles P
parent 2: white flower: two identical alleles p
when crossed: all offspring are Pp. this plant has two different alleles.
how many chromosomes does a pea plant have
14: 7 pairs
what happens if there are two different alleles for the same character? example: two different alleles for flower color?
one allele will be dominant and be visible in the organisms appearance and one allele will be recessive and have no effect on the organisms appearance.
which color is dominant and recessive in mendels experiment?
the purple allele is dominant P and the white allele is recessive p.
what is a genotype?
genotype refers to the genetic makeup of the organism, specifically the combination of alleles.
- PP
- pp
- Pp
the gene for flower color is located on?
chromosome 1 of the pea plant
using the genotype, what can we determine?
using the genotype, we can determine the phenotype.
what is a phenotype?
phenotype is the organisms appearance or observable trait.
PP: purple flower
Pp: purple flower
pp: white flower
heterozygous vs homozygous?
heterozygous: two different alleles for the same gene. Pp
homozygous: two identical alleles for the same gene. PP, pp
what is the law of segregation?
the law of segregation states that two alleles for a character segregate randomly during meiosis so that each gamete receives one or the other with equal likelihood.
what is a punnett square?
a punnett square can be used to predict the allele composition of offspring from a cross between individuals of known genetic makeup
what are the gametes produced by the f1?
for a plant with the genotype Pp, the alleles will segregate randomly into the gametes. as a result, the f1 plant produces two types of gametes.
P and p.
50% P and 50% p.
what are monohybrids?
monohybrids are heterozygous for the character being studied. Pp.
what is a monohybrid cross?
when the monohybrids are crossed, this is called a monohybrid cross.
from the cross of true breeding parents, all of the offspring are?
all of the f1 offspring are monohybrids. when he selfed this generation (f1), he performed a monohybrid cross.
what is a test cross?
a test cross is used to figure out whether an individual with a dominant phenotype is homozygous PP or heterozygous Pp for that trait.
how does the test cross work?
- the organism with the dominant phenotype is in question: PP or Pp?????
- cross the organism with a recessive organism. pp
- if the dominant individual is PP then all of the offspring will be Pp, but if it is Pp, there will be a 50% chance of being Pp and 50% chance of being pp
mendel ALSO did?
crosses with pea plants that differed in two characters. for example: seed color and seed shape.
yellow round seed x green wrinkled seed
Y: yellow seed
y: green seed
R: round seed
r: wrinkled seed
what will the genotype be of the parents: yellow round seed x green wrinkled seed in true breeding?
YYRR x yyrr
what are the gametes produced from each pea plant?
YYRR: YR
yyrr: yr
whats the f1 genotype?
all offspring will be YyRr: heterozygous for both traits resulting in yellow round seeds.
are the f1 plants now monohybrid or dihybrid?
they are dihybrid because they are heterozygous for two characters.
if the F1 generation was selfed, what would happen? YyRr x YyRr =?
YR, Yr, yR, yr are the different possible options.
This is called dihybrid cross.
The phenotypic ratio:
9:3:3:1 in the f2.
