genes & allelesgenes & alleles genotype & phenotypegenotype & phenotype homozygous...
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Genes & Alleles Genotype & Phenotype Homozygous & Heterozygous
Created by
Sima Mathew
and
Jennifer Dietz
Gregor Mendel known as::THE FATHER OF GENETICS.
- laid the foundations for the SCIENCE OF GENETICS through his study of inheritance patterns of traits in pea plants.
What is heredity or inheritance? Passing of traits from parent to offspring
or from one generation to the next.
Genes are the coded instructions that define our traits.
How are genes inherited? Humans have 2 sets of chromosomes for a total of
46 chromosomes. Each parent contributes only 1 set of chromosomes to their child.
When a sperm cell (23 chromosomes) and an egg cell (23 chromosomes) join during fertilization, it results in a zygote (46 chromosomes).
What is a trait? Notable feature or quality in a person.
What are the two types of traits? Physical traits are traits that can be
seen such as eye or hair color Behavioral traits demonstrate the way
one acts such as “the fetching behavior of golden retrievers”.
Phenotype Phenotype is another word for physical
trait (in other words, it describes how someone looks)
Examples of phenotypic words are:tall, short, brown hair, straight hair, fat, skinny, fair skin, freckles, etc.
Can you think of anymore? On your notes, write at least 4 phenotypic
words that describe YOU!
REMEMBER!! Phenotype describes things you can see!!!
What do you think person’s phenotype would be?
How would you describe this phenotype?
Remember?? REMEMBER: Mom gives you one half of your genes, and your dad gives you the other half….
sperm + egg = YOU!
Together, these two genes (one from mom and one from dad) represent your genotype
Each gene is represented by one letter.
Genotype Genotype is the genetic makeup of an
organism’s traits represented by letters
Genotype codes for phenotype
T = tall
t = short
Two different forms of the same gene =
The factors that carry all traits =
Example
Gene = height Alleles = tall; short
Example
Gene = eye color Alleles = green, blue, brown
Example
Gene – hair texture Alleles – straight, wavy, curly
Example
Gene – thumb Alleles – hitchhiker’s thumb, straight thumb
Dominant vs. Recessive Think of a person who never lets you
talk during a conversation – that person DOMINATES the conversation.
A Dominant Allele: allele that is expressed (the one that you see).
A Recessive Allele: allele that is masked or hidden (not shown)
Which allele is expressed over another and represented by a capital letter?
Which allele is usually masked or appears less in the population and represented by a lowercase letter?
Dominant or Recessive?
A
F
r
h
G
t
d
Check Yourself
A – dominant
F - dominant
r – recessive
h - recessive
G - dominant
t - recessive
d - recessive
When both alleles are the SAME it is called
When the alleles are DIFFERENT it is called
B = brown hair b = red hair
homozygous for brown hair
heterozygous for brown hair
homozygous for red hair
HOMOZYGOUS HETEROZYGOUS
Homozygous or Heterozygous?
RRJjttHhaa
Check Yourself
RR - homozygousJj - heterozygoustt - homozygous
Hh - heterozygousaa - homozygous
You inherit two alleles for each gene (trait).
1 from MOM! 1 from DAD! PHENOTYPE –
physical characteristics that you SEE
Ex. Straight hair, red hair, freckles, lactose intolerant, tall, blue eyes
GENOTYPE – genetic makeup represented by letters
Ex. RR, Tt, Ffgg, YyEePp
Principle of Dominance: when there is a dominant allele and a recessive allele inherited together for a particular gene, the dominant allele will ALWAYS be expressed.
Mendel’s 1st Law of Inheritance
Dominant Brown
hairallele
Recessiveredhair
allele
Express the dominant allele for brown hair