Transcript Sex Cells and Inheritance

Sex Cells and Inheritance
Cells- more on the nucleus
Animal and plant cells contain a nucleus.
The nucleus controls cell activities
including cell division. It also contains the
genetic information needed to produce a
new cell.
The information is organized into units
called genes.
Our genes are on chromosomes
Unravelling a
chromosome:
Access
excellence
Chromosomes and Genes
Chromosomes come in pairs.
Human body cells have 23 pairs of chromosomes.
This gives a diploid number of 46.
Human gametes (sperm and egg cells)
contain 23 chromosomes. This is the
haploid number.
Reproduction Revision
Complete the following sentences
Pupil Activity
Another name for sperm and egg cells is
gametes
________
These sex cells join to make one cell
during fertilization
__________
This cell grows into a baby by
multiplying
& dividing
__________________
many times.
Each body cell in the baby contains 23
____
pairs of chromosomes.
One of the chromosomes in each pair
comes from the mother
_______, the other
father
from the _______
Human Life Cycle
Diploid
Zygote
46
fertilization
Haploid
Sperm
23
Haploid
Egg
23
Adult
46
Genes
A characteristic is controlled by the two
forms of a gene present in an individual.
(but the particular combinations are limited by
the genetic makeup of your parents).
The different forms of a gene are called
alleles.
Genetics Buzzwords
physical
appearance of an
organism.
the set of genes (alleles)
that an organism
possesses
different forms
of the same
gene
when two alleles
(gene types) are
identical
when the two alleles
are different
allele which controls
the characteristic
whenever it is
present.
BB or Bb
allele whose characteristics only show up
when it is present on both chromosomes
bb
Boy or Girl?
The sex of a child is
determined by specific
chromosomes called X
and Y chromosomes.
In humans, each male gamete may have an X
or a Y chromosome, while each female
gamete has an X chromosome.
Female
Male
Body cells are
XX
All X
Body cells are
XY
gametes
X or Y
Mother
Father
XX
XY
X
X
Offspring:
Male or
female?
X
X
gamete
X
X
Y
XX
XX
XY
XY
This can also be shown and
combinations worked out using a
Punnett square:
Y
1:1 ratio
male to
female
offspring
Genes and Genotypes
• Genotype:
set of genes that an
organism possesses
• Each organism has two forms of the same
gene
-one inherited from mother
-one inherited from father
• We can say that ‘Organisms possess two
alleles for each different gene’
Genotypes and Symbols
Each allele is represented by a letter
-capital letter if the allele is dominant (A)
-lower case letter if the allele is recessive
(a)
Each organism will have two letters
-1 represents the allele it receives from its
mother
-1 represents the allele it receives from its
father
Height in Pea Plants
T = tall (dominant)
t = short (recessive)
A pea plant can be:
TT = homozygous tall
Tt = heterozygous tall (because T is
dominant to t)
tt = homozygous short
Gene combinations
The simplest genetic cross involves one
characteristic and is called a monohybrid cross.
In this the parents (P) are crossed (bred) with
each other, and the offspring (F1 generation)
observed and counted.
Parents Phenotypes
Genotypes
Gametes
Tall
(Bred
with)
TT
X
all T
F1 genotype
F1 phenotype
Dwarf
tt
all t
Tt
all tall