Genetics Notes PowerPoint-contains meiosis and karyotyping

Download Report

Transcript Genetics Notes PowerPoint-contains meiosis and karyotyping

Genetics and Heredity
Mitosis Review
• Occurs in Somatic Cells (regular body cells)
• Cells are diploid (2 of each chromosome)
• This is asexual reproduction
• One parent produces two daughter cells
• All are identical!!!
Asexual Reproduction
• One parent
• Offspring are identical to parent/ No genetic
• Examples: Vegetative propagation, budding,
• Why is this beneficial?
– Fast
– If it is not broke, don’t fix it!
Sexual Reproduction
• Two parents
• Offspring are different from parents
• Genetic Variation
• Why is this beneficial?
– Produces new traits that can help offspring
• Diploid
– A cell with two of each chromosome (2n)
• Haploid
– A cell with one of each chromosome. (n)
• Meiosis
– Process that reduces the number of chromosomes to
half the number in the original cell.
– Produces haploid cells called gametes.
Occurs in sex cells (gametes)
Cells are haploid (chromosome # is cut in half)
Sexual reproduction
Produces 4 cells that are different
The Law of Independent Assortment states that the
chromosomes in a cell will separate (sort) themselves differently
each time egg and sperm are formed.
This means no siblings are alike unless they are identical twins!!
What happens after gametes are
• Fertilization
– Gametes join to create a diploid cell with a full
set of chromosomes.
– Sperm and Egg form a zygote.
• Does this happen in plants and fungus???
Karyotypes / 3.2
• Karyotypes are pictures of a person’s chromosomes.
You can see all 46 chromosomes.
• Normal human karyotypes have 46 chromosomes or
23 pairs.
• 22 pairs are autosomal chromosomes
1 pair are the sex chromosomes
– Females XX
– Males XY
Chromosomes and karyotypes
• Humans have 46 chromosomes in every
cell of their body. Those 46 chromosomes
are actually 23 pairs of chromosomes.
• 23 come from Mom’s egg
• 23 come from Dad’s sperm
• Remember meiosis???
Chromosome Abnormality Nondysjuctions
• Change in a persons chromosomes.
• Chromosomes can be broken, deleted or
– Remember: There is a lot of DNA in one
chromosome. Chromosome mutations can affect
MANY genes.
• Caused by nondisjunction: chromosomes do
not separate correctly during meiosis.
Examples of Chromosomal Abnormalities
Downs Syndrome
– Caused by: Nondisjunction/Trisomy
– Characteristics: Facial differences, heart defects, mental
– Trisomy 21
• Turner’s Syndrome
– Caused by: Nondisjunction/Monosomy
– Monosomy of the sex chromosomes
– X ___
• Klinefelter’s Syndrome
– Caused by: Nondisjunction/Trisomy
– Trisomy of the sex chromosomes
Detecting Chromosomal Mutations
• Pre-natal
– Amniocentesis: remove a sample of the amniotic
fluid surrounding the fetus.
– Chorionic Villi Sampling: Sample tissue near the
• These can be used to create a karyotype.
Gregor Mendel
• Research on heredity-passing of
characteristics from parents to offspring.
• Studied science and statistics.
• Based most of his studies on peas plants.
• Observed characteristics of pea plants:
Plant height: long or short
Pod color: green or yellow
Seed structure: smooth or wrinkled
Seed color: yellow or green
Flower color: purple or white
What did Mendel observe?
• When he planted seeds from purple
flowering plants some offspring had purple
flowering plants and others had white
flowering plants.
• When he planted smooth seeds he had
plants that produced smooth seeds and some
plants that produced wrinkled seeds.
• Mendel discovered there were 2 forms of each trait/gene.
Each form of a trait or gene is called an allele. Each parent
gives one allele for each trait. So individuals have two
• Mendel began to realize that one allele could “cover up” the
other allele.
• Dominant and recessive alleles.
One allele is dominant and is always expressed
One allele is recessive and is “covered up” by the other
• How/When do we get these traits?
– Law of segregation: a pair of factors is separated during gamete
– This means: Alleles for each gene separate to different gametes
during meiosis.
• The traits you express are your phenotype.
• Alleles show your genotype. The actual genetic make-up.
Relationship between genes and alleles
• A gene is the DNA that codes for a characteristic. The
alleles are the versions of that trait.
Ex. Plant Height (trait/gene)
T=Tall, t=short (alleles)
Flower Color (trait/gene)
P=purple, p=white (alleles)
• Always use ONE letter to represent a gene. Use capital
letters for dominant, lower case letters for recessive.
• Homozygous (“homo” means same)- genotype where the
organism has two of the same alleles for a trait.
– Pure-breeding or True-breeding
– TT or tt
• Heterozygous (“hetero” means different)-genotype
where the organism has two different alleles for a trait.
– Hybrid or Carrier
– Tt
• When alleles are combined they may or may not be
expressed (shown)
• Dominant traits are always expressed.
• Recessive traits are sometimes expressed. Only when
the organism has two recessive alleles. Homozygous
• Rabbits
– B: Big Feet, b: small feet
– F: Floppy ears, f: straight ears
– Bk: Black rabbits (dominant), Br: Brown rabbits
• Show the F1 generation of a monohybrid cross between a
rabbit that is homozygous for floppy ears and a
heterozygous rabbit.
• Cross-offspring from two parents
– Monohybrid looks at one trait
P generations-parents
F1 generation-first offspring from parents
F2 generation-offspring from F1
Selfed/Self-fertilization-cross with one just
like itself
• Test Cross-figure out an unknown genotype
• Green pod color in peas is dominant to yellow pod color.
What offspring are possible from a cross between a GG
plant and a Gg plant?
• B represents black feathers and b represents white
feathers in wrens. What are the possible genotypes and
phenotypes of the F1 from a cross between a
homozygous black wren and homozygous white wren?
• Deafness in dogs is caused by a recessive allele. A deaf
dog is crossed with a hearing dog and some of the
puppies are deaf. Write the genotypes of the parent
• A woman is a carrier for the disease PKU. Her husband
is healthy. What are the chances they will have a child
with PKU?
Types of Dominance
• The type of dominance we have been studying is
complete dominance.
– Two phenotypes are possible.
• Incomplete dominance: When the F1 generation could
have a phenotype completely different from the parents.
– Three phenotypes are available for each trait. The third
phenotype is a mix of the other two.
– Example
• Codominance: When the F1 generation could have a
phenotype completely different from the parents.
– Three phenotypes are available for each trait. The third
phenotype shows both of the other two.
– Example
• Complete Dominance A-D
• Incomplete Dominance E
• Codominance F
• U5HW2 #1 and #2
• Polyallele Traits (Multiple Allele)
Several possible alleles for one trait.
Results in 4-5 phenotypes
Ex. Blood Types (polyallele and codominance)
Blood Type Chart and practice in your notes.
• Polygenic Traits
– Characteristics controlled by two or more genes.
– Genotype: TtGGEe
– Phenotype: More dominant alleles = the more extreme
of a trait.
– Ex. Eye color is determined by the combination of
approx. 3 genes.
Sex-linked Trait
• Last set of notes in Types of Inheritance!!!
• Sex Linkage (these are complete dominance)
– X-linked: genes located on the X chromosome
– Y-linked: genes located on the Y chromosome
– The presence of a gene on a sex chromosome is called a
sex-linked trait
• Ex. Eye color is an X-linked trait in fruit flies. Red
is the dominant allele for this trait. Therefore white
eyed females will only produce white eyed male
• Hemophilia is an X-linked recessive trait. Show the
punnet square between a normal male and a female
who carries the trait for hemophilia. What are the
chances they will have a child with hemophilia?
• Add the activity sheet to your notes and
complete. (10 minutes)
• Work on U5HW2 and Vocabulary
• Pull up/ Print Study Guide for Monday.