Transcript Introduction to Genetics

General Genetics
(Practical Session)
BIO221
Lecturer
Alshehri, Dokhnah Saeed
First lab
Introduction to Genetics
and
MENDEL’S FIRST LAW
 Introduction
to Genetics.
 Mendelian Inheritance.
 Basic Genetic Concepts & Terms.
 Class Activities.
 Some practical Exercises.
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Genetics is a branch of biology which deals
with transmission of characters from one
generation to the next.
Recent advances in cytological studies
demonstrated that hereditary characters are
determined by certain factors, traits, or
genes located on the chromosome.
Each gene is found in a fixed position on a
particular chromosome.
Each person has 2 copies of every gene—one
copy from mom and a second copy from dad.
These copies may come in different
variations, known as alleles, that express
different traits.
For example, 2 alleles in the gene for
freckles are inherited from mom and dad:
– allele
– allele
– child
allele
from mom = has freckles (F)
from dad = no freckles (f)
has the inherited gene pair of alleles, Ff (F
from mom and f allele from dad).
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The basic laws of
heredity were first
formed during the
mid-1800’s by Gregor
Mendel. Because his
work laid the
foundation to the
study of heredity,
Mendel is referred to
as “The Father of
Genetics.”

The term genotype the genes present in
the DNA of an organism. We will use a pair
of letters (ex: Tt or YY or ss, etc.) to
represent genotypes for one particular trait.
There are always two letters in the genotype
because (as a result of sexual reproduction)
one code for the trait comes from mama
organism & the other comes from papa
organism, so every offspring gets two codes
(two letters).
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When we have two capital or two
lowercase letters in the GENOTYPE (ex: TT
or tt) it's called HOMOZYGOUS ("homo"
means "the same"). Sometimes the term
"PURE" is used instead of homozygous.
When the GENOTYPE is made up of one
capital letter & one lowercase letter (ex:
Tt) it's called HETEROZYGOUS ("hetero"
means "other"). Just to confuse you, a
heterozygous genotype can also be
referred to as HYBRID. OK?
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Let's Summarize:
Genotype = genes present in an organism
(usually abbreviated as two letters)
TT = homozygous = pure
Tt = heterozygous = hybrid
tt = homozygous = pure
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The term phenotype refers to the final
expression of all inherited information in
the individual, or its total characteristic
features. In other wards, how the trait
physically shows-up in the organism. If you
wanted to know the simplest way to
determine an organism's phenotype ? Look
at it. Examples of phenotypes: blue eyes,
brown fur, striped fruit, yellow flowers.
In each organism, paired or homologous chromosomes
are present, there are 2 genes for every character; one
gene on each chromosome.
The cells of the organism divided by reduction division
to give the gametes.
In each gamete there is a single gene for every
character.
When these gametes unite together to form zygotes,
each zygote will again have diploid number of
chromosomes.
The two genes located in two corresponding location on
2 chromosomes are called allels.
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1. Which of the following is a possible
abbreviation for a genotype?
A. BC
B. Pp
C. Ty
D. fg
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1. Which of the following is a possible
abbreviation for a genotype?
A. BC
B. Pp
C. Ty
D. fg
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2-Which of the following pairs is not correct?
A. kk = hybrid
B. hybrid = heterozygous
C. heterozygous = Hh
D. homozygous = RR
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2-Which of the following pairs is not correct?
A. kk = hybrid
B. hybrid = heterozygous
C. heterozygous = Hh
D. homozygous = RR
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3- The genes present in an organism
represent the organism's __________.
A. genotype
B. phenotype
C. physical traits
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3- The genes present in an organism
represent the organism's __________.
A. genotype
B. phenotype
C. physical traits
Match the genetic terms to their corresponding parts
of the illustration.
• base pair
• cell
• chromosome
• DNA
• double helix*
• genes
• nucleus
Illustration Source: Talking
Glossary of Genetic Terms
http://www.genome.gov/glossary.cfm?key=chromoso
me
nucleus
chromosome
cell
base
pair
DNA
genes
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H
describes how some traits are
passed from parents to their children.
The traits are expressed by g
, which are
small sections of DNA that are coded for
specific traits.
Genes are found on ch
___.
Humans have two sets of
_ (hint: a
number) chromosomes—one set from each
parent.
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Heredity describes how some traits are
passed from parents to their children.
The traits are expressed by genes, which are
small sections of DNA that are coded for
specific traits.
Genes are found on chromosomes.
Humans have two sets of 23 chromosomes—
one set from each parent.
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 Dominant
and Recessive Genes:
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Alleles that mask or hide other alleles, such as the
“tall” allele, are said to be dominant.
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A recessive allele, such as the short allele, is masked,
or covered up, whenever the dominant allele is present.
 Mendel
crossed red pea plants
with white ones. The F1 plants
were all red. Give the genotypes
and phenotypes of the F1 and F2
generation produced.
A
brown-eyed man marries a
blue-eyed woman, and they have
eight children , all brown-eyed.
What are the genotypes of all the
individuals in the family?
A
blue-eyed man, both of whose
parents were brown-eyed, marries
a brown-eyed woman. They have
one child, who is blue-eyed. What
are the genotypes of all the
individuals mentioned?