CHROMOSOMES - REVIEW

Why we look somewhat like our parents, but not exactly. Human Chromosomes Why we look somewhat like our parents, but not exactly.

Every parent has traits that are similar and different from her child. Why do this mother and daughter look alike in some ways? Why do they look different in some ways? Remember when we did the picture matching activity? You matched kids with their parents by looking at how they were alike and different. You may have seen similarities in eye color, shape of the face, how far the ears stick out and the shape of noses. You also saw that people have their head in the same place, one nose on the front of the head, two ears sticking out either side of the head and a mouth below the nose. How do we get to be the way we are? The study of genetics looks at how we inherit traits from our parents.

Chromosomes Found in the nucleus Contain our genes (made of DNA) Held together by a structure called a centromere.

How Many Chromosomes Do I Have? Human Body cells have 46 chromosomes (23 pairs) Human Gametes (sex cells) have 23 chromosomes. Always half the number as the body cells.

Why??? Why do you think gametes (sex cells) always have exactly half the number of chromosomes as a body cell.

Chromosome number Every organism has its own specific number of chromosomes Examples: Human = 46 chromosomes or 23 pairs Dog = 78 chromosomes or 39 pairs Goldfish = 94 chromosomes or 47 pairs Lettuce = 18 chromosomes or 9 pairs

Look at this body cell. How many chromosomes does it contain? _____ How many pairs of chromosomes? __

Identifying chromosomes Chromosomes can be identified by: Their size Their shape (the position of the centromere) Banding patterns of genes produced by specific stains Chromosomes are analysed by organising them into a KARYOTYPE (shown to theright)

Development and chromosomes The karyotypes of males and females are not the same Females have two large X chromosomes Males have a large X and a small Y chromosome The X and the Y chromosomes are called sex chromosomes The sex chromosomes are placed at the end of the karyotype

The inheritance of gender Mother Father XX XY Meiosis Sex cells X X X Y X Y XX XY Possible children Fertilization Chance of a girl (XX) 50% Chance of a boy (XY) 50%

Which Set of Human Chromosomes Below Belongs to a Male and Which Set Belongs to a Female?

Chromosomal Abnormalities Abnormal development can be associated with wrong chromosome numbers e.g. People who develop Down’s syndrome have trisomy 21 (an extra chromosome 21)

What’s Wrong With This Person’s Chromosomes?

And This Person’s?

Klinefelter Syndrome Persons with Klinefelter syndrome have: male genitalia more than one X chromosome (usually XXY, or a 47,XXY karyotype)

Figure 7-7b The karyotypes and phenotypic depictions of individuals with (a) Klinefelter syndrome (47,XXY) and (b) Turner syndrome (45,X).

Turner Syndrome Persons with Turner syndrome usually have: a single X chromosome no Y chromosome (45,X karyotype) female genitalia

Normal Human Karyotype

A Somatic Cell is a Body Cell

Sex Cells Always Have Half the Number of Chromosomes as Body Cells

What Can Studying The Karyotype of a Person Tell Me About That Person?

Mitosis Mitosis is the process in which a cell divides to form two new cells with identical chromosomes (genes/DNA) Mrs. Camp 7th Grade Life Science 23

How do little elephants grow up to be BIG elephants?

Why do animals shed their skin?

Mitosis begins after fertilization 1 cell becomes 2 cells, 2 cells become 4 cells…4 cells become 8 cells…etc…until trillions of cells

Why do cells make more cells? Three reasons why cells reproduce by asexual reproduction: 1. For Growth 2. To Repair Damaged Cells 3. To Replace Old Cells